Cleanup networking functional tests dummy conf

Due to the fact that the dummies used for the functional tests are
treated just like nics, ifcfg files for them remain after the
functional tests are completed. This patch adds a module teardown
action that restores the networking configuration file status
previous to running the tests.

Patch Set 2:
- Moved the teardown to module level for symmetry.

Change-Id: I7ad2c1b17f6faf5ba12841a385c7eba72fa51d0b
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/16329
Reviewed-by: Giuseppe Vallarelli <gvallare@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>