set default python to python3

Set the default python to python3 except for the py27 environment. We
have to set that explicitly to override the new default.

As part of updating the pep8 job to run python 3 we need to remove the
use of the python 2 builtin unicode(). We can use six.text_type() to
produce the same result until we drop python 2 support.

Change-Id: I43c03aeb73bb8a246115400bcbd9a0a68708abd9
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

oslo_i18n/tests/utils.py

@@ -36,7 +36,7 @@ class NoDeepCopyObject(object):
             return str(self.value)
     else:
         def __unicode__(self):
-            return unicode(self.value)
+            return six.text_type(self.value)
 
     def __deepcopy__(self, memo):
         raise TypeError('Deep Copy not supported')

tox.ini

@@ -3,6 +3,7 @@ minversion = 2.0
 envlist = py35,py27,pep8
 
 [testenv]
+basepython = python3
 install_command = pip install {opts} {packages}
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
@@ -10,6 +11,9 @@ deps =
  -r{toxinidir}/requirements.txt
 commands = python setup.py testr --slowest --testr-args='{posargs}'
 
+[testenv:py27]
+basepython = python2.7
+
 [testenv:pep8]
 deps =
   -r{toxinidir}/test-requirements.txt
@@ -54,7 +58,6 @@ commands = pip-missing-reqs -d --ignore-module=oslo_i18n* --ignore-file=oslo_i18
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:lower-constraints]
-basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt