Add adb enable-verity

Note that it is *easy* to break your phone with this feature. It is
not a bug that reenabling verity after changing one byte of the system
partition stops the device booting.

(cherry-pick of 57e10c5ba4d71a977acc58a47528a682e5351539.)

Bug: 18529433
Change-Id: I632e91281884471a362960f1ba30312d2669b8ff
6 files changed