[RigoDaemon] acquire UpdatesNotificationResourceLock in non blocking mode

We cannot sleep with the activity mutex held without affecting
parallelism so badly. Otoh, we cannot wleep on UpdatesNotificationResourceLock
without affecting 3rd party clients in a way that we would starve them
for a while. So, try to acquire the file lock in non blocking mode
and if it fails, reschedule a new call as soon as the same lock is
freed (exclusive acquire succeeds). This assumes that if the lock
is held back, we will just re-do the whole trick again and again.