Make stop_swift() more robust for Grenade

stop_swift() wasn't calling screen_stop() so the pid files and screen
sessions were not being cleaned up.  DevStack doesn't really care but
Grenade does for the 'base' copy of DevStack.  This should be backported
to stable/havana for this reason.

Change-Id: Ib5afb321cef2b7ad74e69a3fd0d1dad469f78b11
Merge branch 'deprecate-opts' into dt-test
Merge branch 'stop-swift-redux' into dt-test
Merge branch 'set-conf-dir-1' into dt-test
Merge branch 'set-conf-dir-2' into dt-test
Merge branch 'test-service-functions' into dt-test
Merge branch 'move-create-accounts' into dt-test