Extend maintenance config option

[wimpers]

Since openvstorage/framework#2010 we have an edit config option for backends. This ticket is to gather ideas to extend this config wizard.

• Amount of maintenance agents deployed for this backend
• Change the schedule for the ALBA backend verifictaion process
• time after which broken osds are repaired

[matthiasdeblock]

Changing the load of the maintenance.
https://github.com/openvstorage/alba_ee/blob/master-ee/cfg/maintenance_demo.json#L14

Default value is 10.