Last set of subunit2 patches

[Jelmer Vernooij]

Hi Andrew,

The attached patches fix the last issue with my subunit2 branch. I'm just
sending the patches you haven't reviewed earlier; the previous ones are unchanged.

In addition to making sure we always use a testtools/subunit2 combination that is
valid, this moves the remaining python modules from lib/ to third_party/.

The complete branch can also be found as 'for-review/subunit2' at
git://git.samba.org/jelmer/samba.git.

Cheers,

Jelmer