[SPARK-10511] [BUILD] Reset git repository before packaging source distro

The calculation of Spark version is downloading
Scala and Zinc in the build directory which is
inflating the size of the source distribution.

Reseting the repo before packaging the source
distribution fix this issue.

Author: Luciano Resende <lresende@apache.org>

Closes #8774 from lresende/spark-10511.

dev/create-release/release-build.sh

@@ -99,6 +99,7 @@ fi
 DEST_DIR_NAME="spark-$SPARK_PACKAGE_VERSION"
 USER_HOST="$ASF_USERNAME@people.apache.org"
 
+git clean -d -f -x
 rm .gitignore
 rm -rf .git
 cd ..