Enable hieradata ExtraConfig overrides for Controller

Enable hieradata ExtraConfig overrides for Controller

Wires in the ControllerExtraConfig and ExtraConfig parameters so
that they may be used to specify overrides of the default hieradata.

Note if this is used to override values specified via parameters
rather than hard-coded values in puppet/hieradata caution should
be used as the overridden values will always take precendence
regardless of the parameter input, unless the parameter is provided
directly to the Deployment resource applying the manifiest (e.g
not the pattern currently employed in most of t-h-t)

Also note that ControllerExtraConfig takes precedence over the
deployment-wide ExtraConfig.

For example, here's how you would pass a value which disables the
heat-api-cfn service on all controllers. This would be put into an
environment file, then passed to the heat stack-create via an extra
-e option:

parameters:
  controllerExtraConfig:
    heat::api_cfn::enabled: false

Note the parameter capitalization is different in the top-level
overcloud-without-mergepy template for some reason.

Change-Id: I6d6e3e78460308134d95c01892bb242aba70e9ca