Check for merge commit more resiliently

.gitlab-ci.yml

@@ -175,9 +175,11 @@ behave-grafana:
 terminate_droplet_after_merge:
   stage: cleanup
   script: |
-    if [ "$(git cat-file -p HEAD | grep -c '^parent')" -gt 1 ]
+    if [ "$(git show -s --pretty=%p HEAD | wc -w)" -gt 1 ]
     then
-      pipeline=$(git cat-file -p 893aed0e1f1ce02a77b8f2a66ad03c24f09915d9 | grep 'Merge branch' | tr -dc '0-9')
+      subject="$(git show -s --format=%s)"
+      tmp="${subject#*\'}"
+      pipeline="${tmp%%\-*}"
       echo "Current HEAD is a merge commit, removing droplet from related merge request pipeline #${pipeline}."
       python3 -c "import greenhost_cloud; greenhost_cloud.terminate_droplets_by_name(\"^ci-${pipeline}\.\")"
     else