WIP galera-pxc-maint-mode

[alpes214]

Description:
This is branch for fix issue #2656

[Tusamarco]

@Val214 there is a reason for the hostname to be explicit and hardcoded in MySQL_HostGroups_Manager.cpp line 4683?
q=(char *)"UPDATE mysql_servers_incoming SET status=1 WHERE hostname='172.18.0.20' AND port=%d AND hostgroup_id=%d";

[alpes214]

@Val214 there is a reason for the hostname to be explicit and hardcoded in MySQL_HostGroups_Manager.cpp line 4683?
q=(char *)"UPDATE mysql_servers_incoming SET status=1 WHERE hostname='172.18.0.20' AND port=%d AND hostgroup_id=%d";

@Tusamarco This is just a POC. There was no reason for hard coding, just prototyping. I will remove this PR.

Sorry for misleading.

[alpes214]

Closed as POC.