stop timer early if lock acquired

Previously, TryLockTimed would leave the timer running until the duration elapsed. The only use of TryLockTimed is in the host, where it is used with a duration of 1 minute in managedTryLockStorageObligation. This is unlikely to cause problems in practice, but in theory, calling managedTryLockStorageObligation too frequently will eventually exhaust available memory due to the accumulating timers.