Rework mariadb recovery tasks

In recover_cluster.yaml playbook the task to find the highest
seqno/Global Transaction ID is no longer relying only on grastate.dat
Instead it now follows the recommendations from galera cluster website
http://galeracluster.com/documentation-webpages/restartingcluster.html

Closes-Bug: 1682153

Change-Id: I5fc3eaa8baee659576c4c39aef9cfd351c8e9af7