Turn vibrator off explicitly on waveforms when amplitude is zero

This makes sure the drive will be off for the period of time described in the waveform pattern with amplitude = 0.

Bug: 172492945
Test: manual
Change-Id: I604fea474b6b0b56ee6d16cacb4c4fc97cb7516a
Merged-In: I753e4846fce3066b78e818afa5c794b113244ab0