PSA: workaround for segfault when running dnf update in F30

[Jonathan Dieter]

<tl;dr>
librepo-1.9.6 has a major bug that will cause a segfault when a
repository has zchunk metadata.  To temporarily work around the
problem, set zchunk=False in /etc/dnf/dnf.conf or wait until the next
updates push comes out
</tl;dr>

About a week ago, we disabled zchunk metadata in the main F30
repository because of arm-specific compose problems[1].  The problems
were fixed and we enabled zchunk metadata in F30 updates-testing
yesterday, but, in the interval when there were no zchunk-enabled
repositories, librepo-1.9.6 was released, and it has a major bug where
it segfaults whenever dnf update is run on a repository with zchunk
metadata.

We've disabled zchunk metadata for F30 updates-testing and doing a new
push now.

I have submitted a fix[2] for the bug, but for now any F30 users need
to do one of the following:
 * Wait until the next updates push is out.  It won't have zchunk
   metadata, so updates will work normally again.
 * Set zchunk=False in /etc/dnf/dnf.conf.  This will force dnf to fall
   back to non-zchunk metadata, bypassing the bug.

Many apologies for the inconvenience.

Jonathan

[1] https://pagure.io/dusty/failed-composes/issue/1703
[2] https://github.com/rpm-software-management/librepo/pull/148