Wait for pg_hba to be updated before creating user

Puppet tries to create the postgres test user after postgres has been
initialized, but before pg_hba.conf has been updated and the service
restarted.

Fixes Bug 1038956
Merge pull request #2208 from bramwelt/fix-1038956-socorro-vagrant-build

Fix 1038956 - Wait for pg_hba to be updated before creating Postgres test user