There is no record for why we implement the database creation outside
of the role in the playbook, when we could do it inside the role.
Implementing it inside the role allows us to reduce the quantity of
group_vars duplicated from the role, and allows us to better document
the required variables in the role. The delegation can still be done
as it is done in the playbook too.
In this patch we implement a new variable called 'rally_db_setup_host'
which is used in the role to allow delegation of the database setup
task to any host, but defaults to the first member of the galera_all
host group. We also document the variable 'rally_galera_address' which
has been used for a long time, but never documented. A bunch of unused
variables have also been removed.
Change-Id: Ifb89e35e3acaef33ce4ce24b3f5affc6c4e8e494
c4e6c8ce30