Apply os-net-config with a script instead of element

Apply os-net-config with a script instead of element

Wire in os-net-config via a normal script heat deployment, which has the
following advantages:

1. Improved error path, currently o-a-c deployments don't report any
errors, thus hang and eventually the deployment times out

2. It's far more hackable from a deployer perspective, e.g it's
much easier to change the os-net-config options or include a
mapping file

3. Reduces our dependencies on o-a-c (it's only os-net-config and hiera
which requires it), although the script does currently still use oac to
get the metadata IP.

4. May enable passing os-net-config yaml via a json parameter in future,
reducing the need for resource_registry mappings (although we'll have to
support that for backwards compatibility)

The script used is based directly on 20-os-net-config (from t-i-e
at cf94c5e, we can probably improve this now that we have an error path,
but for this initial commit it's a straight copy other than the changes to
replace o-a-c for rendering the json config file.

Co-Authored-By: Steven Hardy <shardy@redhat.com>
Change-Id: I0ed08332cfc49a579de2e83960f0d8047690b97a