releasetools: OutputFile stages files under input dir.

We used to create the intermediate output file as a tempfile, when
adding images to a given zip file. This CL changes OutputFile to write
intermediate files under the given input dir (i.e. OPTIONS.input_tmp
that holds the unzipped files), if the final destination is a zip
archive. This allows image building codes finding the generated images
at consistent locations. The intermediate files will be cleaned up as
part of OPTIONS.input_tmp.

Bug: 122608028
Test: `m dist`
Test: Delete OTA/super*.img from a target_files.zip. Run
      `add_img_to_target_files.py -a` that re-generates split super
      images.
Change-Id: I97903a59fcc0ca5e43bb9b07c3a0b25e9baa92f9