Use single nova-api worker per compute node

Then using nova-network with metadata,
we don't have to spawn so many (processors core
count based) api workers for compute nodes.

Closes-bug: #1377837

Change-Id: I5835a09451d1604f6323a5cb50bfb7babb9304a5
Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>
Merge "Use single nova-api worker per compute node"