[SPARK-19237][SPARKR][CORE] On Windows spark-submit should handle when java is not installed

## What changes were proposed in this pull request?

When SparkR is installed as a R package there might not be any java runtime.
If it is not there SparkR's `sparkR.session()` will block waiting for the connection timeout, hanging the R IDE/shell, without any notification or message.

## How was this patch tested?

manually

- [x] need to test on Windows

Author: Felix Cheung <felixcheung_m@hotmail.com>

Closes #16596 from felixcheung/rcheckjava.

R/pkg/inst/tests/testthat/test_Windows.R

@@ -20,6 +20,7 @@ test_that("sparkJars tag in SparkContext", {
   if (.Platform$OS.type != "windows") {
     skip("This test is only for Windows, skipped")
   }
+
   testOutput <- launchScript("ECHO", "a/b/c", wait = TRUE)
   abcPath <- testOutput[1]
   expect_equal(abcPath, "a\\b\\c")

bin/spark-class2.cmd

@@ -50,7 +50,16 @@ if not "x%SPARK_PREPEND_CLASSES%"=="x" (
 
 rem Figure out where java is.
 set RUNNER=java
-if not "x%JAVA_HOME%"=="x" set RUNNER=%JAVA_HOME%\bin\java
+if not "x%JAVA_HOME%"=="x" (
+  set RUNNER="%JAVA_HOME%\bin\java"
+) else (
+  where /q "%RUNNER%"
+  if ERRORLEVEL 1 (
+    echo Java not found and JAVA_HOME environment variable is not set.
+    echo Install Java and set JAVA_HOME to point to the Java installation directory.
+    exit /b 1
+  )
+)
 
 rem The launcher library prints the command to be executed in a single line suitable for being
 rem executed by the batch interpreter. So read all the output of the launcher into a variable.