tests: Add NetworkTest.testSetupNetworksAddDelkDhcp

Tests adding and deletion of network with dynamically
assigned address.

Patch version 11. Cosmetic refractoring in firewall.py.

Change-Id: I9dbb59f3cd420b2071eb0ec42f9816ab52151bce
Signed-off-by: Petr Benas <pbenas@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/21113
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>