oslotest itself depends on debtcollector and debtcollector depends
on oslotest. That's a cycle dependency which makes bootstrapping the whole
module chain more difficult.
Instead of using oslotest, just use the standard unittest.TestCase class
as base to break the dependency cycle.
Change-Id: Idcbe727883fe2742d62d463bb9a195592aeaba09
da416d64e2