Add a kernel transition to snapuserd.

The initial launch of snapuserd happens in first-stage init, before
sepolicy is loaded, since snapuserd is needed to mount initial
partitions. After sepolicy is loaded, we immediately re-launch snapuserd
in the correct context. This requires a transition similar to init.

The "allow" lines for the kernel happen in permissive mode, since we
need to relabel critical parts of /dev/block in order to re-launch
snapuserd.

Bug: 173476209
Test: OTA applies with ro.virtual_ab.compression.enabled = true
Change-Id: I80184e737ccb558107a14b384a61f7fec31c9428
3 files changed