Split out allNodesConfig SoftwareConfig

Split out allNodesConfig SoftwareConfig

This patch splits out the allNodesConfig config
such that alternate implementation (puppet for example)
can implement their own SoftwareConfig's via a nested stack.

This is controlled by the standard overcloud heat environment.

For os-apply-config deployments the implementation should work the
same as before.

For puppet deployments the implementation uses hiera metadata
to configure rabbit_nodes. The puppet deployment doesn't support
hosts, or freeform sysctl metadata yet so those are the same
for now as well.

Change-Id: I34ae30b1f37aca8b39586f7e350511462d66f694