Restrict database access to nova-compute in singleconductor mode
Restrict database access to nova-compute in singleconductor mode

Change I4820abe57a023050dd8d067c77e26028801ff288 removed access
to the database for the nova-compute process but only in
superconductor mode. Grenade runs in singleconductor mode though
so we are getting tracebacks in nova-compute logs during grenade
runs because nova-compute is running with nova.conf which is
configured with access to the nova API database.

This change handles removing database access for nova-compute
generically to cover both the singleconductor and superconductor
cases.

Change-Id: I81301eeecc7669a169deeb1e2c5d298a595aab94
Closes-Bug: #1812398

nawawi/openstack,dtroyer/devstack,openstack-dev/devstack,dtroyer/devstack,openstack-dev/devstack,nawawi/openstack