Better optimize test runs

This syncs a few changes from ironic's tox.ini:

* Specify minimum tox version as 1.8
* Skips sdist generation
* Don't write bytecode (pyc) when running tests
* Run tests in English so that log messages are consistent

Change-Id: If0b8afb1102d8ee2ba31ea88f1259fbb42143605

tox.ini

@@ -1,9 +1,13 @@
 [tox]
+minversion = 1.8
+skipsdist = True
 envlist = py27,py34,pep8
 
 [testenv]
 usedevelop = True
 setenv = VIRTUAL_ENV={envdir}
+         PYTHONDONTWRITEBYTECODE = 1
+         LANGUAGE=en_US
          TESTS_DIR=./ironic_lib/tests/
 deps = -r{toxinidir}/test-requirements.txt
 commands = ostestr {posargs}