Allow vold to get the DSU status

Currently, the vold detects the factory reset by checking the
metadata encryption key. This logic is only valid when the
device is not in DSU mode. This CL allows vold to get the DSU
status.

Test: run DSU installation on a Pixel device
Bug: 199222795
Change-Id: Ia6ca3b27afd52347b132d7e2d8be244fb9f15e7d
1 file changed