Don't stop n-cpu if in DO_NOT_UPGRADE_SERVICES

To support the partial-ncpu grenade test, if n-cpu is in
DO_NOT_UPGRADE_SERVICES don't stop it.

Requires stable/havana devstack patch: I031707a49974df684cc473737ceb07cecc262c66

Change-Id: Ia63287ffbf36113cc99602d7bdc7ec040d252a6c
Merge "Don't stop n-cpu if in DO_NOT_UPGRADE_SERVICES"