Synchronize DeviceDisconnect in VolumeManager

Sometimes the device would disconnect when attempting to switch devices
which would cause a Null Pointer Exception.

Bug: 116489958
Test: Sanity test switching between devices
Change-Id: I0cd4eeb82564b69af9164cca9019f9463ac44f06
(cherry picked from commit 4b40a547b399e547187818fb7bf5f42a0bcb565e)