Fixed commit of Galera/MySQL for HA

This is the first commit of information on installing
and configuring MySQL to use Galera for high availability
in OpenStack.  It should provide enough information to get
get users going, but may be incomplete. This commit
includes fixes based on comments.

bug #1091889
blueprint #improve-high-availability-support

Change-Id: I1d7861a3264dd6de3b4afa028b683099909bde70