fix(django): retry-based e2e testing (GoogleCloudPlatform#5340)

* WIP - retry-based django e2e testing

* Fixes

* rev trampoline

* format

* revert

* fix

* Workaround: create user in worker, not cloudbuild

permissions do not currently permit cloudbuild to create sqlusers

* minor cleanup

* black

* black is not flake8

* databases cannot be deleted by cloudbuild rn

* remove unused subvar

* cleanup

* Restore setup/cleanup to cloudbuild

* Update retry.sh to handle two-arg failure, ultimate failure

* Change use of retry.sh to be create, or describe/delete

Author: glasnt

run/django/.gcloudignore

@@ -1 +1,2 @@
 .env
+venv