vold: Use Wakelock::tryGet()

Acquiring a wakelock can fail if the suspend service is unavailable.
Explicitly check that wakelock was acquired before performing
operations that require the device to stay on.

Bug: b/179229598
Test: Boot test on Pixel 4 device
Change-Id: If30087223e44098801a31d1bfd239ac22e891abe
4 files changed