nova: call map_cell0 much earlier in the setup
nova: call map_cell0 much earlier in the setup

The map_cell0 command creates a cell mapping record in the
nova_api database, and the nova-manage db sync command
will migrate the db schema for the nova_cell0 database. This
patch takes advantage of that by moving the map_cell0 call
much earlier in the setup process so we get the nova_cell0
db schema migrated at the same time as the main nova db.

This also removes the || true condition around map_cell0
since it's idempotent now due to fix:

aa7b6ebbb254f00fcb548832941ca9dbd3996d9f

Change-Id: Ice4fbb1771270c618b2acbc933d4fbfb6805df81

openstack-dev/devstack,nawawi/openstack,noironetworks/devstack,group-policy/devstack,group-policy/devstack,richliu/devstack,nawawi/openstack,openstack-dev/devstack,dtroyer/devstack,richliu/devstack,dtroyer/devstack,noironetworks/devstack