Switch tox unit test command to use ostestr

This commit switches the tox command to use ostestr instead of
calling testr through setup.py. This is inline with the all the
other OpenStack projects. It also removes requirements.txt from
tox.ini deps as that is redundant, as per:
http://lists.openstack.org/pipermail/openstack-dev/2015-July/069663.html

Change-Id: I8133d233f0fc0e1da2677d43d65056b9b070f867

test-requirements.txt

@@ -1,5 +1,6 @@
 mock
 hacking>=0.9.2,<0.10
 testrepository>=0.0.18
-testtools>=0.9.36,!=1.2.0
+testtools>=1.4.0 # MIT
+os-testr>=0.4.1 # Apache-2.0
 ddt

tox.ini

@@ -1,15 +1,16 @@
 [tox]
-envlist = py27,pep8,py34
+envlist = py34,py27,pep8
 
 [testenv]
 usedevelop = True
 install_command = pip install -U {opts} {packages}
-deps =
-  -r{toxinidir}/requirements.txt
-  -r{toxinidir}/test-requirements.txt
-commands =
-  bash -c "TESTS_DIR=./proliantutils/tests/ python setup.py testr --slowest --testr-args='{posargs}'"
-whitelist_externals = bash
+setenv = VIRTUAL_ENV={envdir}
+         PYTHONDONTWRITEBYTECODE = 1
+         LANGUAGE=en_US
+         LC_ALL=en_US.UTF-8
+         TESTS_DIR=./proliantutils/tests/
+deps = -r{toxinidir}/test-requirements.txt
+commands = ostestr {posargs}
 
 [testenv:pep8]
 basepython = python2.7