Revert "Avoid testtools 0.9.25"

This reverts commit acae86293f7b0bba8fe105779f6f75df3af9ec51.
Testtools upstream is fixed.

Change-Id: Idc5f51bef76e31d627a80c742f5587d51e373d22
Merge "Revert "Avoid testtools 0.9.25""