Handle more nicely when role root is already here

When using postgresql we were handling the fallback if the role root was
already here but this was still printing an error message, try to make
it a bit smarter.

Closes-Bug: #1265477
Change-Id: Ib3768dd182ab968e81038f900550f641b9a2af5c
Merge "Handle more nicely when role root is already here"
Merge branch 'master' of github.com:openstack-dev/devstack