[FIX] gitlab_tools: add validations to the deploy_tests and test_image commands to reduce the chance of errors

1. Fixed the postgres check to correctly retry the check when postgres is starting
2. Added a check that makes sure that the containers are running before starting the tests

Tests:

• Deployv tests:
  Build where all the retries of the container check failed:
  https://git.vauxoo.com/vauxoo-dev/deployv/builds/17552 (since I was not able to reproduce this error, I provoked it, so some log messages could be misleading)
  Build where everything went fine:
  https://git.vauxoo.com/vauxoo-dev/deployv/builds/17589

• Images test:
  (I was not able to reproduce the errors found during the builds)