Fix: getting the right screen name in stop-base

There was missing piece from review
https://review.openstack.org/#/c/28637/
Fixing it here. Sleep is added to guarantee the services
are terminated.

Blueprint: blueprint/nightly-upgrade-testing

Change-Id: I71d35ea28410ce6756850fb5e07357712a6a792c
Merge "Fix: getting the right screen name in stop-base"