[MINOR][R] Add knitr and rmarkdown packages/improve output for version info in AppVeyor tests

## What changes were proposed in this pull request?

This PR proposes three things as below:

**Install packages per documentation** - this does not affect the tests itself (but CRAN which we are not doing via AppVeyor) up to my knowledge.

This adds `knitr` and `rmarkdown` per https://github.com/apache/spark/blob/45824fb608930eb461e7df53bb678c9534c183a9/R/WINDOWS.md#unit-tests (please see https://github.com/apache/spark/commit/45824fb608930eb461e7df53bb678c9534c183a9)

**Improve logs/shorten logs** - actually, long logs can be a problem on AppVeyor (e.g., see https://github.com/apache/spark/pull/17873)

`R -e ...` repeats printing R information for each invocation as below:

```
R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
Copyright (C) 2016 The R Foundation for Statistical Computing
Platform: i386-w64-mingw32/i386 (32-bit)

R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under certain conditions.
Type 'license()' or 'licence()' for distribution details.

  Natural language support but running in an English locale

R is a collaborative project with many contributors.
Type 'contributors()' for more information and
'citation()' on how to cite R or R packages in publications.

Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.
```

It looks reducing the call might be slightly better and print out the versions together looks more readable.

Before:

```
# R information ...
> packageVersion('testthat')
[1] '1.0.2'
>
>

# R information ...
> packageVersion('e1071')
[1] '1.6.8'
>
>
... 3 more times
```

After:

```
# R information ...
> packageVersion('knitr'); packageVersion('rmarkdown'); packageVersion('testthat'); packageVersion('e1071'); packageVersion('survival')
[1] ‘1.16’
[1] ‘1.6’
[1] ‘1.0.2’
[1] ‘1.6.8’
[1] ‘2.41.3’
```

**Add`appveyor.yml`/`dev/appveyor-install-dependencies.ps1` for triggering the test**

Changing this file might break the test, e.g., https://github.com/apache/spark/pull/16927

## How was this patch tested?

Before (please see https://ci.appveyor.com/project/HyukjinKwon/spark/build/169-master)
After (please see the AppVeyor build in this PR):

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #18336 from HyukjinKwon/minor-add-knitr-and-rmarkdown.

appveyor.yml

@@ -26,6 +26,8 @@ branches:
 
 only_commits:
   files:
+    - appveyor.yml
+    - dev/appveyor-install-dependencies.ps1
     - R/
     - sql/core/src/main/scala/org/apache/spark/sql/api/r/
     - core/src/main/scala/org/apache/spark/api/r/
@@ -38,12 +40,8 @@ install:
   # Install maven and dependencies
   - ps: .\dev\appveyor-install-dependencies.ps1
   # Required package for R unit tests
-  - cmd: R -e "install.packages('testthat', repos='http://cran.us.r-project.org')"
-  - cmd: R -e "packageVersion('testthat')"
-  - cmd: R -e "install.packages('e1071', repos='http://cran.us.r-project.org')"
-  - cmd: R -e "packageVersion('e1071')"
-  - cmd: R -e "install.packages('survival', repos='http://cran.us.r-project.org')"
-  - cmd: R -e "packageVersion('survival')"
+  - cmd: R -e "install.packages(c('knitr', 'rmarkdown', 'testthat', 'e1071', 'survival'), repos='http://cran.us.r-project.org')"
+  - cmd: R -e "packageVersion('knitr'); packageVersion('rmarkdown'); packageVersion('testthat'); packageVersion('e1071'); packageVersion('survival')"
 
 build_script:
   - cmd: mvn -DskipTests -Psparkr -Phive -Phive-thriftserver package