Split out Nova software config

This is a step towards supporting pluggable software configurations
in the heat templates. By moving compute-config out of compute.yaml
we make it possible to define alternate implementations by
changing the OS::TripleO::Compute::SoftwareConfig value in the
overcloud-resource-registry.yaml heat environment file.

Co-Authored-By: Steve Hardy <shardy@redhat.com>

Change-Id: I250dc1a8c02626cf7d1a5d2ce92706504ec0c7de
Merge "Split out Nova software config"