[SPARK-12910] Fixes : R version for installing sparkR

Testing code:
```
$ ./install-dev.sh
USING R_HOME = /usr/bin
ERROR: this R is version 2.15.1, package 'SparkR' requires R >= 3.0
```

Using the new argument:
```
$ ./install-dev.sh /content/username/SOFTWARE/R-3.2.3
USING R_HOME = /content/username/SOFTWARE/R-3.2.3/bin
* installing *source* package ‘SparkR’ ...
** R
** inst
** preparing package for lazy loading
Creating a new generic function for ‘colnames’ in package ‘SparkR’
Creating a new generic function for ‘colnames<-’ in package ‘SparkR’
Creating a new generic function for ‘cov’ in package ‘SparkR’
Creating a new generic function for ‘na.omit’ in package ‘SparkR’
Creating a new generic function for ‘filter’ in package ‘SparkR’
Creating a new generic function for ‘intersect’ in package ‘SparkR’
Creating a new generic function for ‘sample’ in package ‘SparkR’
Creating a new generic function for ‘transform’ in package ‘SparkR’
Creating a new generic function for ‘subset’ in package ‘SparkR’
Creating a new generic function for ‘summary’ in package ‘SparkR’
Creating a new generic function for ‘lag’ in package ‘SparkR’
Creating a new generic function for ‘rank’ in package ‘SparkR’
Creating a new generic function for ‘sd’ in package ‘SparkR’
Creating a new generic function for ‘var’ in package ‘SparkR’
Creating a new generic function for ‘predict’ in package ‘SparkR’
Creating a new generic function for ‘rbind’ in package ‘SparkR’
Creating a generic function for ‘lapply’ from package ‘base’ in package ‘SparkR’
Creating a generic function for ‘Filter’ from package ‘base’ in package ‘SparkR’
Creating a generic function for ‘alias’ from package ‘stats’ in package ‘SparkR’
Creating a generic function for ‘substr’ from package ‘base’ in package ‘SparkR’
Creating a generic function for ‘%in%’ from package ‘base’ in package ‘SparkR’
Creating a generic function for ‘mean’ from package ‘base’ in package ‘SparkR’
Creating a generic function for ‘unique’ from package ‘base’ in package ‘SparkR’
Creating a generic function for ‘nrow’ from package ‘base’ in package ‘SparkR’
Creating a generic function for ‘ncol’ from package ‘base’ in package ‘SparkR’
Creating a generic function for ‘head’ from package ‘utils’ in package ‘SparkR’
Creating a generic function for ‘factorial’ from package ‘base’ in package ‘SparkR’
Creating a generic function for ‘atan2’ from package ‘base’ in package ‘SparkR’
Creating a generic function for ‘ifelse’ from package ‘base’ in package ‘SparkR’
** help
No man pages found in package  ‘SparkR’
*** installing help indices
** building package indices
** testing if installed package can be loaded
* DONE (SparkR)

```

Author: Shubhanshu Mishra <[email protected]>

Closes #10836 from napsternxg/master.

R/README.md

@@ -1,6 +1,16 @@
 # R on Spark
 
 SparkR is an R package that provides a light-weight frontend to use Spark from R.
+### Installing sparkR
+
+Libraries of sparkR need to be created in `$SPARK_HOME/R/lib`. This can be done by running the script `$SPARK_HOME/R/install-dev.sh`.
+By default the above script uses the system wide installation of R. However, this can be changed to any user installed location of R by setting the environment variable `R_HOME` the full path of the base directory where R is installed, before running install-dev.sh script.
+Example: 
+```
+# where /home/username/R is where R is installed and /home/username/R/bin contains the files R and RScript
+export R_HOME=/home/username/R
+./install-dev.sh
+```
 
 ### SparkR development
 

R/install-dev.sh

@@ -35,12 +35,19 @@ LIB_DIR="$FWDIR/lib"
 mkdir -p $LIB_DIR
 
 pushd $FWDIR > /dev/null
+if [ ! -z "$R_HOME" ]
+  then
+    R_SCRIPT_PATH="$R_HOME/bin"
+   else
+    R_SCRIPT_PATH="$(dirname $(which R))"
+fi
+echo "USING R_HOME = $R_HOME"
 
 # Generate Rd files if devtools is installed
-Rscript -e ' if("devtools" %in% rownames(installed.packages())) { library(devtools); devtools::document(pkg="./pkg", roclets=c("rd")) }'
+"$R_SCRIPT_PATH/"Rscript -e ' if("devtools" %in% rownames(installed.packages())) { library(devtools); devtools::document(pkg="./pkg", roclets=c("rd")) }'
 
 # Install SparkR to $LIB_DIR
-R CMD INSTALL --library=$LIB_DIR $FWDIR/pkg/
+"$R_SCRIPT_PATH/"R CMD INSTALL --library=$LIB_DIR $FWDIR/pkg/
 
 # Zip the SparkR package so that it can be distributed to worker nodes on YARN
 cd $LIB_DIR