Fix trove guest confing to ignore user os_admin

This value of ignore_users in the guest config needs to be set
correctly to ignore the local os_admin user for the trove functional
tests to pass in a devstack-gate environment.

Change-Id: Ia31dfe8f2eab4b24790b6be0dbc474cf50f39afa
Merge "Fix trove guest confing to ignore user os_admin"