Add variables for active-passive Galera HA proxy

Add variables and data mappings needed to configure Galera HAProxy in an
active-passive model due to compatibility issues between Galera
configured with multiple active writers and certain SQL statements used
in OpenStack code.

Change-Id: I09111b406edf3799e01b7172956d08d84d40f526
Partial-Bug: #1321734
Merge "Add variables for active-passive Galera HA proxy"