Put py34 first in the env order of tox
Put py34 first in the env order of tox

To solve the problem of "db type could
not be determined" on py34 we have to run first the py34 env to, then, run
py27. This patch puts py34 first on the tox.ini list of envs to avoid this
problem to happen.

Change-Id: I966264e04fbe9441d90c48645df5e6216ca0f4d5
Closes-bug: #1489059

openstack/openstack-doc-tools,openstack/openstack-doc-tools