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.

Because flake8 runs under python 3, where the type "long" has been
merged into int(), we have to ignore the error from the undefined name
in one of the tests.

Change-Id: I86ae7f83d17724d74bae7102dd1775eceb82599d
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

oslo_versionedobjects/tests/test_fields.py

@@ -160,7 +160,7 @@ class TestString(TestField):
         self.coerce_good_values = [
             ('foo', 'foo'), (1, '1'), (1.0, '1.0'), (True, 'True')]
         if six.PY2:
-            self.coerce_good_values += [(long(1), '1')]
+            self.coerce_good_values += [(long(1), '1')]  # noqa
         self.coerce_bad_values = [None]
         self.to_primitive_values = self.coerce_good_values[0:1]
         self.from_primitive_values = self.coerce_good_values[0:1]

tox.ini

@@ -3,6 +3,7 @@ minversion = 2.0
 envlist = py35,py27,pep8
 
 [testenv]
+basepython = python3
 setenv =
     VIRTUAL_ENV={envdir}
     BRANCH_NAME=master
@@ -12,6 +13,9 @@ deps =
   -r{toxinidir}/test-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 @@ deps = -r{toxinidir}/doc/requirements.txt
 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