Fix multiple issues with MariaDB handling

These affected both deploy (and reconfigure) and upgrade
resulting in WSREP issues, failed deploys or need to
recover the cluster.

This patch makes sure k-a does not abruptly terminate
nodes to break cluster.
This is achieved by cleaner separation between stages
(bootstrap, restart current, deploy new) and 3 phases
for restarts (to keep the quorum).

Upgrade actions, which operate on a healthy cluster,
went to its section.

Service restart was refactored.

We no longer rely on the master/slave distinction as
all nodes are masters in Galera.

Closes-bug: #1857908
Closes-bug: #1859145
Change-Id: I83600c69141714fc412df0976f49019a857655f5