Including tasks has a performance penalty when compared with importing
tasks. The nova-cell role uses include_tasks twice when generating
certificates and keys for libvirt TLS. While a dynamic include makes
sense here for a non-default feature, we can use one include rather than
two with the same effect. Since this task runs against compute nodes the
overhead is significant.

See [1] for benchmarks of include_tasks and import_tasks.

[1] https://github.com/stackhpc/ansible-scaling/blob/master/doc/include-and-import.md

Partially-Implements: blueprint performance-improvements

Change-Id: Ic687d2f7d4625aede386e576ebb174da72142756

The idea is to factor out a role for deploying Nova related services
to cells. Since all deployments use cells, this role can be used
in both regular deployments which have just cell0 and cell1,
and deployments with many cells.

Partially Implements: blueprint support-nova-cells
Change-Id: Ib1f36ec0a773c384f2c1eac1843782a3e766045a

To securely support live migration between computenodes we should enable
tls, with cert auth, instead of TCP with no auth support.

Implements: blueprint libvirt-tls

Change-Id: I22ea6233933c840b853fdcc8e03400b2bf577271