Better optimize test runs
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

openstack/ironic-lib,NaohiroTamura/ironic-lib