Merge pull request cms-sw#135 from degano/pr_last_release

PR tests now automatically takes the latest available release.

run-pr-tests

@@ -35,8 +35,8 @@ popd
 export PATH=$PWD/cms-git-tools:$PATH
 which git-cms-merge-topic
 git config --global user.github cmsbuild
-RELEASE_NAME=`date +$RELEASE_FORMAT`
 export SCRAM_ARCH=$ARCHITECTURE
+RELEASE_NAME=`scram l -c $RELEASE_FORMAT | tail -1 | awk '{print $2}'`
 scram project $RELEASE_NAME
 cd $RELEASE_NAME
 eval `scram run -sh`