Fix race condition in HalVibratorHelper

Make methods that handle vibration command records synchronized so tests
can load copies for assertion white the execution is logging commands.

This is particularly useful in VibrationThreadTest, where we can make
conditional waits based on the commands sent to the HAL.

Fix: 429228739
Test: VibrationThreadTest
Flag: EXEMPT test only
Change-Id: Idb328644506b9591e0d9f7fde0df6a3a0e879731