store filesystem config info in target files at build time

Store a dump of the desired uid/gid/mode for every system file in the
target_files zip.  Modify ota_from_target_files to use this stored
information when it is available, instead of running fs_config from
the current client (which might be out of sync from the one where the
target_files zip was built).

b/2516887 - New android_filesystem_config.h needed

Change-Id: I8409a0265d1d50daad9c2bc033c99b74b8931b20