Remove references to unittest2 from the Compute tests

* Since we're dropping support for Python 2.6, these references
  should be removed. If that can't be done, then we should add
  unittest2 to the pip-requires of this project

Change-Id: I80a8724d8e98647cb8c079fe0d19c762c1c5ffd8
Merge "Remove references to unittest2 from the Compute tests"