Compute: drive NW configuration via software conf

This example extends the compute software configuration
so that heat metadata is used to model the os-net-config
YAML (ultimately JSON) directly. The existing
os-net-config element already supports this format.

Configuring the physical network layer in this manner
would supplant the ever growing list of Heat parameters
that we have and is something that could be automatically
generated via tuskar.

The default is to use net-config-noop.yaml which
will pass no config metadata into the os-net-config
element which will essentially disable it in favor
of using parameters w/ init-neutron-ovs.

Change-Id: I30f325b1751caaef5624537e63ee27c2e418d5c8