In first-stage init, libsnapshot needs to know how to wait for device
paths, since ueventd isn't running yet. We do this by passing a callback
wrapping BlockDevInitializer.
Bug: 173476209
Test: device boots into first-stage init after full VABC ota
Change-Id: I9a87f98824e65a9379cb0b99c001e28cccd9d205
This allows init to easily ensure misc devices other than device-mapper
are present.
Bug: 154536437
Test: manual test
Change-Id: I49495684edee322f9787ce7ab7f79d0e8060171d
This will make it possible to re-use in second-stage init.
Bug: 150315914
Test: first-stage init boots
Change-Id: I6a0f13d5c71ab5529a76751f68ac0f15834323d1