Disable libdnf5 plugins during tests

[evan-goode]

See https://pagure.io/fedora-ci/general/issue/538#comment-1001814.

Disable libdnf5 plugins during tests so newly-installed libdnf5 don't alter the behavior of DNF5 and break subsequent tests. We want to test whether packages (including libdnf5 plugins) are installable/upgradable/downgradable/removable, not whether they work correctly when executed, in the testing environment, without being configured, etc.

As mentioned in the comment, a better solution might be to only disable plugins which are not installed by default. One way to do this would be to list currently-enabled plugins:

#!/usr/bin/env python3
import libdnf5
base = libdnf5.base.Base()
base.load_config()
base.setup()
print(",".join(p.get_name() for p in base.get_plugins_info() if p.is_loaded()))

and then run DNF5 with dnf5 --disable-plugin=\* --enable-plugin=$MYPLUGINLIST. But that would be a more involved change, I think we'd need to update everywhere $YUMDNFCMD is called.

[evan-goode]

The issue was moved to https://forge.fedoraproject.org/ci/tickets/issues/538.

[LecrisUT]

To avoid making permanent changes on a machine, consider putting it in the installability tmt test instead: https://github.com/fedora-ci/installability-pipeline/blob/2673077b28449d11cd5cbc5f7dcdbf976c5ebdd4/installability.fmf#L9-L20