Major refactor of Percona playbooks

The previous playbook was not entirely reliable. Often tests would fail
in the CI and in development.  This refactor seeks to fix that. At the
same time, that code had all lived under playbooks. Broke this out into
a set of roles.
Update percona playbook with host categories

Update the playbook to use 3 stanzas. The first 'common' stanza provides
what we need wrt fact gathering. The second now stands up the primary
node and the third is able to filter out the primary from the host
groupings.
Adding defaults to the percona-server role

Adding percona.replication = True to the percona-server role defaults.
Merge pull request #221 from craigtracey/percona_refactor

Major refactor of Percona playbooks