Add a configuration file for tox (http://testrun.org/tox/)

Python 2.6 and 2.7 interpreters are added to PATH, you can execute the following. Each virtual environment will be made and a test will be run.

$ tox

NOTE: py33 was failure because dependence packages are not worked on Python3 (At least: Eventlet).

Signed-off-by: Satoshi Kobayashi <satoshi-k@stratosphere.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>