test: Allow check-packagekit to run against existing machine
test: Allow check-packagekit to run against existing machine

- Drop machine provision from PackageCase, and replace it with a lighter
  hack to disable the (non-working on our test VMs) DNS server, so that
  PackageKit does not run into long timeouts. Restrict this to Debian,
  it does not cause problems on other OSes.
- Backup/restore the original repositories, to avoid totally destroying
  the testbed.
- Backup/restore and move away PackageKit's transaction database, as an
  existing one breaks the test.
- Clean up all installed test packages.

Closes #11333

deryni/cockpit,mvollmer/cockpit,cockpit-project/cockpit,deryni/cockpit,garrett/cockpit,martinpitt/cockpit,deryni/cockpit,garrett/cockpit,deryni/cockpit,deryni/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,deryni/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,deryni/cockpit,cockpituous/cockpit,cockpituous/cockpit,garrett/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,garrett/cockpit,cockpit-project/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,garrett/cockpit,mvollmer/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,cockpituous/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,cockpituous/cockpit