OTA: Specify targets for ota_all

By default, ota_all will create incremental updates for all folders
listed in MK_OTA_INPUT. If only specific targets are required, do:

ota_all TYPE target1,target2,target3

TYPE: RELEASE, NIGHTLY, EXPERIMENTAL, UNOFFICIAL
target: device names, separated by ','

Change-Id: I7be81acfcec98d70024a229b4705e4c80b1b40e0
OTA: Clean up verifier after flashing (1/2)

Change-Id: I8079328d9d143be905bc340cedda1299b28d8af7