DeskClock: restore vibrations after screen is turned off

android.server.VibratorService forcefully clears out all vibrations
after the screen is turned off. If an alarm is going off, we do not want
the power button to only stop vibrations.

Change-Id: Ic7bc556d7cf5529b23b482c34e986853ad4ba4f2
Signed-off-by: Roman Birg <roman@cyngn.com>