Don't run check pipeline if the user is allowd test pipeline

This is the ugly way to test it, but it's better than nothing.
Constantly having jenkins-bot run the tests twice and the
overhead is just too much:
- Wasted processing time for Jenkins and Zuul running lots of
  jobs twice for no reason, occupying the queue.
- Double the notifications from Jenkins
- Double the comments from jenkins-bot
- Race condition bug where V+1 (check: success) can sometimes
  overrides V-2 (test: failure).

Bug: 43391
Change-Id: Ic9a3411406fafdb0de19ed20d7e717b20280fd7d