Rename mCameraGestureTriggered to mPowerButtonLaunchGestureTriggered.

As part of supporting using the double tap power button gesture to
launch wallet instead of camera, this CL changes the camera gesture-specific
variable names to generic power button gesture.

Test: mp droid
Bug: 378469025
Flag: android.service.quickaccesswallet.launch_wallet_option_on_power_double_tap

Change-Id: I47fc66db5de038143324890a72842c0b601e8c03