Use os-testr for py34 tox target

os-testr has a blacklist we can use to specify which
tests to avoid. It uses "testr run --parallel" so tests
are run in parallel as well. We also get rid of the
huge list of tests in tox.ini into a separate file.

<soap_box>
The reason for using a black list is that when new tests
are being added, they are automatically either fixed to
work under python34 or added to a well known list of
tests so whoever is working on python34 can try to fix
those tests over a period of time. Hoping really that
this black list shrinks over time quickly. This is also
a pool of low hanging tasks that folks when they have
some time to pull a few tests from here and fix them.
</soapbox>

Bumps number of tests executed from 5606 to 7206

Depends-On: Ib5e682d0380cf7bc5e288a1e4d125379b452fa92
Change-Id: Ib641bb0f7553eb7704b419b9d00f86174f6d831d

test-requirements.txt

@@ -17,6 +17,7 @@ sphinx!=1.2.0,!=1.3b1,<1.3,>=1.1.2
 sphinxcontrib-seqdiag
 oslosphinx>=2.5.0 # Apache-2.0
 oslotest>=1.10.0 # Apache-2.0
+os-testr>=0.4.1
 testrepository>=0.0.18
 testtools>=1.4.0
 tempest-lib>=0.8.0