Prefer --fast for skipping all checks

Closes https://git.autonomic.zone/coop-cloud/abra/issues/169

.drone.yml

@@ -32,10 +32,6 @@ steps:
       - run shellcheck
       - run flake8
       - run unit tests
-    when:
-      event:
-        exclude:
-          - pull_request
 
   - name: trigger downstream builds
     image: plugins/downstream
@@ -51,10 +47,6 @@ steps:
       - run flake8
       - run unit tests
       - publish image
-    when:
-      event:
-        exclude:
-          - pull_request
 
   - name: notify on failure
     image: plugins/matrix