Post-boot transition to/from acting as a master or slave HC must be done with management op execution locked out

As part of WFCORE-338, a Candidate Domain Controller can shift between acting a master or acting as slave without requiring a reload or reboot.

However, after initial boot, a DCC can be handling management requests. Any transition between acting as a master or slave to the other role must ensure that in-process management requests are not disrupted and that no new management requests are able to access the management model or runtime services until the transition is complete. As a practical matter this likely means that the transition task(s) must acquire the exclusive management lock and hold it until the transition is complete.