The server resource type, OS::TripleO::Server can now be mapped per role
instead of globally. This allows users to mix baremetal
(OS::Nova::Server) and deployed-server (OS::Heat::DeployedServer) server
resources in the same deployment.
blueprint pluggable-server-type-per-role
Change-Id: Ib9e9abe2ba5103db221f0b485c46704b1e260dbf