Pack base_fs files into target_files.zip.

Pack the base_fs files ({system,vendor}.map) into target_files.zip,
which would be needed when rebuilding the images at signing.

Reset the base_fs paths to point to the files in META/.

Also add blk_alloc_to_base_fs into otatools.zip.

Bug: 27698960
Change-Id: If4eb274b3f3d839c4365624f46f0dc89bd2fa440