nova: improve compute service registration failure handling

If any nova compute service fails to register itself, Kolla Ansible will
fail the host that queries the Nova API. This is the first compute host
in the inventory, and fails in the task:

    Waiting for nova-compute services to register themselves

Other hosts continue, often leading to further errors later on. Clearly
this is not idea.

This change modifies the behaviour to query the compute service list
until all expected hosts are present, but does not fail the querying
host if they are not. A new task is added that executes for all hosts,
and fails only those hosts that have not registered successfully.

Alternatively, to fail all hosts in a cell when any compute service
fails to register, set nova_compute_registration_fatal to true.

Change-Id: I12c1928cf1f1fb9e28f1741e7fe4968004ea1816
Closes-Bug: #1940119