Move remounting of app dirs to onVolumeStateChangedInternal

ag/10648863 made the callback asyncrouns and broke the bookkeeping for
mFuseMountedUser. This makes sure the mFuseMountedUser is updated
sequentially and that access is properly guarded by mLock.

Bug: 152612342
Test: atest AdoptableHostTest
Test: atest FuseDaemonHostTest
Test: Manually verified that zygote mounts directories for new launches
Change-Id: Ibc514de96e7bc86e249dd86814abc4d358feef0a