do not bzip2 debootstrap.tar

The APK itself is compressed, and the bzip2 file is hard to make
deterministic.
force timestamps of debootstrap.tar and contents to that of the .deb

Use the timestamp from the downloaded .deb file to set all of the files and
the .tar file itself to the same timestamp.  This should make the creation
of the .tar file deterministic.  So far, it does seem to always be the same
size, but there are still some other small differences.
REBASE do not bzip2 debootstrap.tar
REWORD force timestamps of debootstrap.tar and contents to that of the .deb