Custom RM principal causes zookeeper HA state store to be inaccessible

HDP 2.6 stack introduced settings for ACLs on the Yarn Resource Manager HA state store. In `yarn-site/yarn.resourcemanager.zk-acl` the ACL user is set to `rm`.

If this user name does not match the primary component of the Yarn RM Kerberos principal in `yarn-site/yarn.resourcemanager.principal`, then Yarn is unable to access the state store and RM will stop immediately after start.

During the Kerberos wizard there needs to be a check to see if these settings are out of sync. Or, the zk-acl setting needs to somehow reference the principal and extract the primary root through a variable.