As 'vm' is not proper for platform, we now used server_type
to replace platfrom. As server_type can be vm or baremetal(bm) etc.
The idea here is to provide a way for magnum to discover and interact
with templates meant to build bays. Template definition discovery is
done through python entry_points, and each class lists the bay_types
it can provide. Each template definition contains a mapping of magnum
object attributes and heat template parameters/outputs.
This will be useful for not only allowing different CoEs, OSes, and
platforms. But can also provide the discovery mechanism for templates
once they are pulled into their own repository.
Partial-Implements: bp multiple-bay-templates