Move BlockDifference into common and make its script generation code
more complete, so that it can be use by releasetools.py to do diffs on
baseband images.
Bug: 16984795
Change-Id: Iba9afc1c7755458ce47468b5170672612b2cb4b3
Replace the xdelta/xz-based block OTA generation with a new system
based on the existing bsdiff/imgdiff tools.
Bug: 16984795
Change-Id: Ia9732516ffdfc12be86260b2cc4b1dd2d210e886