[SPARK-17651][SPARKR] Set R package version number along with mvn

## What changes were proposed in this pull request?

This PR sets the R package version while tagging releases. Note that since R doesn't accept `-SNAPSHOT` in version number field, we remove that while setting the next version

## How was this patch tested?

Tested manually by running locally

Author: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

Closes apache#15223 from shivaram/sparkr-version-change.

dev/create-release/release-tag.sh

@@ -60,12 +60,27 @@ git config user.email $GIT_EMAIL
 
 # Create release version
 $MVN versions:set -DnewVersion=$RELEASE_VERSION | grep -v "no value" # silence logs
+# Set the release version in R/pkg/DESCRIPTION
+sed -i".tmp1" 's/Version.*$/Version: '"$RELEASE_VERSION"'/g' R/pkg/DESCRIPTION
+# Set the release version in docs
+sed -i".tmp1" 's/SPARK_VERSION:.*$/SPARK_VERSION: '"$RELEASE_VERSION"'/g' docs/_config.yml
+sed -i".tmp2" 's/SPARK_VERSION_SHORT:.*$/SPARK_VERSION_SHORT: '"$RELEASE_VERSION"'/g' docs/_config.yml
+
 git commit -a -m "Preparing Spark release $RELEASE_TAG"
 echo "Creating tag $RELEASE_TAG at the head of $GIT_BRANCH"
 git tag $RELEASE_TAG
 
 # Create next version
 $MVN versions:set -DnewVersion=$NEXT_VERSION | grep -v "no value" # silence logs
+# Remove -SNAPSHOT before setting the R version as R expects version strings to only have numbers
+R_NEXT_VERSION=`echo $NEXT_VERSION | sed 's/-SNAPSHOT//g'`
+sed -i".tmp2" 's/Version.*$/Version: '"$R_NEXT_VERSION"'/g' R/pkg/DESCRIPTION
+
+# Update docs with next version
+sed -i".tmp3" 's/SPARK_VERSION:.*$/SPARK_VERSION: '"$NEXT_VERSION"'/g' docs/_config.yml
+# Use R version for short version
+sed -i".tmp4" 's/SPARK_VERSION_SHORT:.*$/SPARK_VERSION_SHORT: '"$R_NEXT_VERSION"'/g' docs/_config.yml
+
 git commit -a -m "Preparing development version $NEXT_VERSION"
 
 # Push changes