Add minimum master capability for draining and deactivation states

Since we are adding new fields to the registry to represent agent draining/deactivation, we cannot allow downgrades of masters while such features are in use.

A new minimum capability should be added to the registry with the appropriate documentation:
https://github.com/apache/mesos/blob/663bfa68b6ab68f4c28ed6a01ac42ac2ad23ac07/src/master/master.cpp#L1681-L1688
http://mesos.apache.org/documentation/latest/downgrades/