Support for stale master in case of restart

In case where replication monitor gets a stale master status (slaves are down) and maxscale gets restarted, master loses the stale master status and no writes can happen.

Suggest to track this or at least open the possibility to set stale master manually (not possible through maxadmin yet)

Scenario
A is master and die
B and C was valide slave

B is elected as new master

A is stopped and get some unknow sate

Remaining slave C

• Can be , stopped
• Can still be attached to A
• Can be reset replication

In all scenarios an external arbitrator forcing B as master , should enable routing to B via maxscale

We propose to introduce a new state masterforced
masterforced wins the master status if it conflict with mastermonitored
when both state become equal then maxscale can re trust the monitoring information and reset masterforced with a simple masterflag