THRIFT-4351: change DOCKER_ env vars for travis integration to work better,
ready for enabling job on PRs

This closes #1397
diff --git a/build/docker/run.sh b/build/docker/run.sh
index b54924b..1fe19d5 100755
--- a/build/docker/run.sh
+++ b/build/docker/run.sh
@@ -21,7 +21,7 @@
 set -e
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-. $SCRIPT_DIR/vars.sh
+DOCKER_TAG=$DOCKER_REPO:$DISTRO
 
 printenv | sort