Don't require the exclusive management lock to run the "kill" or "destroy" ops on the HC

EDITED: The below isn't quite accurate (ServerShutdownHandler does acquire the exclusive lock) and we need to consider carefully the repurcussions of not doing that. No one should work on this without discussing it with me first.

ServerProcessHandlers.execute is calling context.getServiceRegistry(true) in order to trigger an authorization check. Problem is that also means the exclusive lock needs to be acquired.

There are other ways to handle this. See https://github.com/wildfly/wildfly-core/blob/master/server/src/main/java/org/jboss/as/server/operations/ServerShutdownHandler.java#L90 for a similar case.

Side issue: the constructor for ServerProcessHandlers should be package-protected. Same with the "serverInventory" field. This isn't a bug, it's just being tidy and locking things down as much as possible.