Disable elasticsearch validation on all stable-2.1* branches

Elasticsearch tests are flaky in all legacy stable-2.1*
branches. Prevent the Elasticsearch-related failures to
impact the other changes validations.

Change-Id: Idafebf8b9ceb34cb63e06501f4d31af789299179
diff --git a/jenkins/gerrit-bazel-verifier-test.sh b/jenkins/gerrit-bazel-verifier-test.sh
index 7e519bd..60eb70c 100644
--- a/jenkins/gerrit-bazel-verifier-test.sh
+++ b/jenkins/gerrit-bazel-verifier-test.sh
@@ -8,7 +8,7 @@
 echo '----------------------------------------------'
 
 TEST_TAG_FILTERS="-flaky"
-if [ "$TARGET_BRANCH" == "stable-2.16" ]
+if [[ "$TARGET_BRANCH" = stable-2.1* ]]
 then
   TEST_TAG_FILTERS="$TEST_TAG_FILTERS,-elastic"
 fi