init: Fix ordering of second-stage snapuserd transition.

Running snapuserd before early-init means ueventd is missing, which
means we can't use WaitForFile() when dm-user misc devices are created.
Fix this by starting the transition after early-init.

Bug: 173476209
Test: full OTA with VABC applies and boots
Change-Id: Ice594cceb44981ae38deb82289d313c14726c36b