Revert "Revert "adb: support /oem partition""

This reverts commit 6084a0124f868c7ec43f6c415a27a168f27ff694.

The original build breakage is fixed by (a) building the verity
code for eng builds as well as userdebug builds and (b) moving
the exported remount service functions into a new header file.

Change-Id: Ice0c4f97d4db38ab7eb333c7a6e56bbd11123f5b
8 files changed