Add test cases to validate resource's mandatory fields and functions

Any heat resource plugin is expected to have the following fields

Required:
support_status
properties_schema
handle_create()
handle_delete()
resource_mappings()

optional:
default_client_name
entity
attributes_schema

It becoming an common pitfalls that developer implements the first patch of the new resources and reviewer started to comment on the missing things. It involves extra effort.

so if we could provide an schema validation for resource plugins as one of unit test cases, which makes developer to make the resource plugin to be stable before submit for review.