Add new base classes for Bay and Cluster to inherit from.
Add new tests for cluster and cluster_template code.
Leaves all commands in-place and adds new cluster-related
commands for magnumclient.
Add deprecation decorator and messages for bay/baymodel.
Implements: blueprint rename-bay-to-cluster
Change-Id: I64e1aa6a71b109687568005655c6de55f86fad29
