Migrated unit tests to testtools

Main changes:
* testtools checks that base setUp is called
* assertRaises doesn't return context
* testtools inherits from unittest (not unittest2) and doesn't have
  specific compare functions in py2.6

Notes:
* Integration tests will be tracked separately (bp: it-testtools)
* Migration to oslotest will be tracked separately (bp: oslotest)
* bug #1325108 is out of scope of this CR

Implements blueprint: ut-testtools
Closes-Bug: #1179009

Change-Id: I85f0ea1aa972ff68ddd1817ec936a8c26312f041