[SPARK-18807][SPARKR] Should suppress output print for calls to JVM methods with void return values

## What changes were proposed in this pull request?

Several SparkR API calling into JVM methods that have void return values are getting printed out, especially when running in a REPL or IDE.
example:
```
> setLogLevel("WARN")
NULL
```
We should fix this to make the result more clear.

Also found a small change to return value of dropTempView in 2.1 - adding doc and test for it.

## How was this patch tested?

manually - I didn't find a expect_*() method in testthat for this

Author: Felix Cheung <felixcheung_m@hotmail.com>

Closes #16237 from felixcheung/rinvis.

(cherry picked from commit 3e11d5bf)
Signed-off-by: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

R/pkg/R/SQLContext.R

@@ -634,7 +634,7 @@ tableNames <- function(x, ...) {
 cacheTable.default <- function(tableName) {
   sparkSession <- getSparkSession()
   catalog <- callJMethod(sparkSession, "catalog")
-  callJMethod(catalog, "cacheTable", tableName)
+  invisible(callJMethod(catalog, "cacheTable", tableName))
 }
 
 cacheTable <- function(x, ...) {
@@ -663,7 +663,7 @@ cacheTable <- function(x, ...) {
 uncacheTable.default <- function(tableName) {
   sparkSession <- getSparkSession()
   catalog <- callJMethod(sparkSession, "catalog")
-  callJMethod(catalog, "uncacheTable", tableName)
+  invisible(callJMethod(catalog, "uncacheTable", tableName))
 }
 
 uncacheTable <- function(x, ...) {
@@ -686,7 +686,7 @@ uncacheTable <- function(x, ...) {
 clearCache.default <- function() {
   sparkSession <- getSparkSession()
   catalog <- callJMethod(sparkSession, "catalog")
-  callJMethod(catalog, "clearCache")
+  invisible(callJMethod(catalog, "clearCache"))
 }
 
 clearCache <- function() {
@@ -730,6 +730,7 @@ dropTempTable <- function(x, ...) {
 #' If the view has been cached before, then it will also be uncached.
 #'
 #' @param viewName the name of the view to be dropped.
+#' @return TRUE if the view is dropped successfully, FALSE otherwise.
 #' @rdname dropTempView
 #' @name dropTempView
 #' @export

R/pkg/R/context.R

@@ -87,8 +87,8 @@ objectFile <- function(sc, path, minPartitions = NULL) {
 #' in the list are split into \code{numSlices} slices and distributed to nodes
 #' in the cluster.
 #'
-#' If size of serialized slices is larger than spark.r.maxAllocationLimit or (200MB), the function 
-#' will write it to disk and send the file name to JVM. Also to make sure each slice is not 
+#' If size of serialized slices is larger than spark.r.maxAllocationLimit or (200MB), the function
+#' will write it to disk and send the file name to JVM. Also to make sure each slice is not
 #' larger than that limit, number of slices may be increased.
 #'
 #' @param sc SparkContext to use
@@ -379,5 +379,5 @@ spark.lapply <- function(list, func) {
 #' @note setLogLevel since 2.0.0
 setLogLevel <- function(level) {
   sc <- getSparkContext()
-  callJMethod(sc, "setLogLevel", level)
+  invisible(callJMethod(sc, "setLogLevel", level))
 }

R/pkg/R/sparkR.R

@@ -427,7 +427,7 @@ sparkR.session <- function(
 #' @method setJobGroup default
 setJobGroup.default <- function(groupId, description, interruptOnCancel) {
   sc <- getSparkContext()
-  callJMethod(sc, "setJobGroup", groupId, description, interruptOnCancel)
+  invisible(callJMethod(sc, "setJobGroup", groupId, description, interruptOnCancel))
 }
 
 setJobGroup <- function(sc, groupId, description, interruptOnCancel) {
@@ -457,7 +457,7 @@ setJobGroup <- function(sc, groupId, description, interruptOnCancel) {
 #' @method clearJobGroup default
 clearJobGroup.default <- function() {
   sc <- getSparkContext()
-  callJMethod(sc, "clearJobGroup")
+  invisible(callJMethod(sc, "clearJobGroup"))
 }
 
 clearJobGroup <- function(sc) {
@@ -484,7 +484,7 @@ clearJobGroup <- function(sc) {
 #' @method cancelJobGroup default
 cancelJobGroup.default <- function(groupId) {
   sc <- getSparkContext()
-  callJMethod(sc, "cancelJobGroup", groupId)
+  invisible(callJMethod(sc, "cancelJobGroup", groupId))
 }
 
 cancelJobGroup <- function(sc, groupId) {

R/pkg/inst/tests/testthat/test_sparkSQL.R

@@ -576,7 +576,7 @@ test_that("test tableNames and tables", {
   tables <- tables()
   expect_equal(count(tables), 2)
   suppressWarnings(dropTempTable("table1"))
-  dropTempView("table2")
+  expect_true(dropTempView("table2"))
 
   tables <- tables()
   expect_equal(count(tables), 0)
@@ -589,7 +589,7 @@ test_that(
   newdf <- sql("SELECT * FROM table1 where name = 'Michael'")
   expect_is(newdf, "SparkDataFrame")
   expect_equal(count(newdf), 1)
-  dropTempView("table1")
+  expect_true(dropTempView("table1"))
 
   createOrReplaceTempView(df, "dfView")
   sqlCast <- collect(sql("select cast('2' as decimal) as x from dfView limit 1"))
@@ -600,7 +600,7 @@ test_that(
   expect_equal(ncol(sqlCast), 1)
   expect_equal(out[1], "  x")
   expect_equal(out[2], "1 2")
-  dropTempView("dfView")
+  expect_true(dropTempView("dfView"))
 })
 
 test_that("test cache, uncache and clearCache", {
@@ -609,7 +609,7 @@ test_that("test cache, uncache and clearCache", {
   cacheTable("table1")
   uncacheTable("table1")
   clearCache()
-  dropTempView("table1")
+  expect_true(dropTempView("table1"))
 })
 
 test_that("insertInto() on a registered table", {
@@ -630,13 +630,13 @@ test_that("insertInto() on a registered table", {
   insertInto(dfParquet2, "table1")
   expect_equal(count(sql("select * from table1")), 5)
   expect_equal(first(sql("select * from table1 order by age"))$name, "Michael")
-  dropTempView("table1")
+  expect_true(dropTempView("table1"))
 
   createOrReplaceTempView(dfParquet, "table1")
   insertInto(dfParquet2, "table1", overwrite = TRUE)
   expect_equal(count(sql("select * from table1")), 2)
   expect_equal(first(sql("select * from table1 order by age"))$name, "Bob")
-  dropTempView("table1")
+  expect_true(dropTempView("table1"))
 
   unlink(jsonPath2)
   unlink(parquetPath2)
@@ -650,7 +650,7 @@ test_that("tableToDF() returns a new DataFrame", {
   expect_equal(count(tabledf), 3)
   tabledf2 <- tableToDF("table1")
   expect_equal(count(tabledf2), 3)
-  dropTempView("table1")
+  expect_true(dropTempView("table1"))
 })
 
 test_that("toRDD() returns an RRDD", {