This includes some lightweight refactoring to avoid code
duplication.

This patch is made to be backportable to Train.
We now include Ansible in testing since Ussuri so the comments
about the bool filter are wrong.

Change-Id: Ia2e0f7f24988763bacfeafefb7977021f5949f4e
Closes-bug: #1848941

This moves the Nova Cells filters alongside the service filters
for ease of testing.

Partially Implements: blueprint support-nova-cells
Change-Id: I32d35c065812c6b46c64bacdf283a0bdad0f8a0f

This patch adds initial support for deploying multiple Nova cells.

Splitting a nova-cell role out from the Nova role allows a more granular
approach to deploying and configuring Nova services.

A new enable_cells flag has been added that enables the support of
multiple cells via the introduction of a super conductor in addition to
cell-specific conductors. When this flag is not set (the default), nova
is configured in the same manner as before - with a single conductor.

The nova role now deploys the global services:

* nova-api
* nova-scheduler
* nova-super-conductor (if enable_cells is true)

The nova-cell role handles services specific to a cell:

* nova-compute
* nova-compute-ironic
* nova-conductor
* nova-libvirt
* nova-novncproxy
* nova-serialproxy
* nova-spicehtml5proxy
* nova-ssh

This patch does not support using a single cell controller for managing
more than one cell. Support for sharing a cell controller will be added
in a future patch.

This patch should be backwards compatible and is tested by existing CI
jobs. A new CI job has been added that tests a multi-cell environment.

ceph-mon has been removed from the play hosts list as it is not
necessary - delegate_to does not require the host to be in the play.

Documentation will be added in a separate patch.

Partially Implements: blueprint support-nova-cells
Co-Authored-By: Mark Goddard <mark@stackhpc.com>
Change-Id: I810aad7d49db3f5a7fd9a2f0f746fd912fe03917