save file block allocations in target_files

make_ext4fs can now output a file listing the blocks used for each
file in the image.  Request this file and save it in the target_files;
it will be used for future improvements to block OTAs.

Bug: 16984795
Change-Id: Id1e60465e3b5a9d126a7934b4d089cf34d8fec44
3 files changed