Kerberos: during disable, need option skip if unable to access KDC to remove principals

Attempted to disable kerb, fails on step to unkerberize because KDC admin is locked out.

Click retry, can't make it past that.

Need option to skip and finish "disable kerberos" even if Ambari cannot get the principals cleaned up (i.e. cannot access the KDC) Losing access to the KDC and attempting to disable where ambari can't clean-up the principals should be a skip'able step. User should still be able to get to a clean, not-enabled-kerberos-ambari-state w/o accessing the KDC.

Solution
Add a flag to the kerberos-env configuration to specify whether Kerberos identities should be managed by Ambari (true, default) or not (false). This flag is to be overridable via a directive like manage_identities=false when disabling Kerberos, which will skip over any KDC administrative processes.