Add tox files from neutron, with a few changes

* ignores warnings about 'print' statements.
* we want to use neutron's tox settings because:
  (1) we want to keep our python standards consistent
  (2) some of these files will probably be moved to our plugin in the
      future

Change-Id: I59ce286df838f737360544e79e93ff278fdbd0b3
Signed-off-by: Joe Mills <joe@midokura.com>