Remove references for unittest2
Remove references for unittest2

unittest2 was needed for python<=2.6, it is time to remove it from
requirements.

Change-Id: Iac22d787af46ad57f24391eae2188b0c74c84299

stackforge/networking-bagpipe-l2,openstack/networking-bagpipe,openstack/networking-bagpipe-l2,stackforge/networking-bagpipe-l2,openstack/networking-bagpipe,openstack/networking-bagpipe-l2