SCRIPTS: publish-release: pass -n to gzip to remove timestamp

SCRIPTS: publish-release: pass -n to gzip to remove timestamp

It just appeared that the tar.gz we put online are not reproducible
because a timestamp is put by default into the archive. Passing "-n"
to gzip is sufficient to remove this timestamp, so let's do it, and
also make the gzip command configurable for more flexibility. Now
issuing the commands multiple times finally results in the same
archives being produced.

This should be backported to supported stable branches.