qmemman: make sure to release lock

Even when handling updated meminfo or domain list something goes wrong,
make sure to release the lock - otherwise the whole qmemman will be
blocked.

qubes/tools/qmemmand.py

@@ -143,11 +143,12 @@ class XS_Watcher(object):
         self.log.debug('acquiring global_lock')
         global_lock.acquire()
         self.log.debug('global_lock acquired')
+        try:
             if force_refresh_domain_list:
                 self.domain_list_changed(refresh_only=True)
 
             system_state.refresh_meminfo(domain_id, untrusted_meminfo_key)
-
+        finally:
             global_lock.release()
             self.log.debug('global_lock released')