Relanding 'update_engine: Add XZ compression for CrOS'

This patch implements XZ compression for Chrome OS. It is only activated
for only delta payload at this point. The XZ compression is typically
slower than Bzip2 to compress, but faster to decompress. However, it
uses slightly higher memory in decompression. It compresses about 5%-10%
better than the current Bzip2.

BUG=chromium:758792
TEST=unittests pass; brillo_update_paylod {generate|verify} passes;

Change-Id: I2fd8f6af30449c779cd2abb061e42ab389913d93
Reviewed-on: https://chromium-review.googlesource.com/872125


Commit-Ready: Amin Hassani <ahassani@chromium.org>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Sen Jiang <senj@chromium.org>