Revert "Refresh directory servers on mount"

This reverts commit 9601b8941119654a4b4dace717b7e1def7af171d since it causes a
dependency cycle. Until a proper fix is in place (an upstream fix to the
directory service's retry behaviour is in the works) the problem can be solved
manually by restarting the Quobyte directory service manually once all devices
have been mounted.