Updated automate method parse_provider_category for host provisioning

Added check for miq_host_provision key
Updated to use defines for return values.

https://bugzilla.redhat.com/show_bug.cgi?id=1121287
@gmcculloug 
Does it make sense to put a category method on the vm base class with a  category (or better named) method defaulting to "unknown"
Then, the "infastructure" vm classes return "infrastructure" for their method via inheritance, and "cloud" vm classes return "cloud" for their method?

I can imagine we have other places where we might do different things based on it's category.

Just a thought.

Everything else looks good.