Merge "DO NOT MERGE: Add the option to reserve headroom for partition images....

Merge "DO NOT MERGE: Add the option to reserve headroom for partition images. This is useful for devices with low disk space with different build variants." into cw-f-dev
am: 1590301a

Change-Id: I85bbf6b85c42ff3e9e69565812f8a2b8a0f41833