aptly: Disable bzip2 compression for index files

The installed aptly version now allows to disable bzip2 compression for
index files. Enable this to speed up aptly publishing, as speed
performance is more important than Package file size in this case.

Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@collabora.com>
5 jobs for collabora/staging in 12 minutes and 12 seconds (queued for 3 seconds)