Fix the gate

Following PyCQA/astroid@206d8a2 we sarted getting a whole bunch of
errors like

    E:266,44: Value 'headers' doesn't support membership test

and

    E:267,25: Value 'headers' is unsubscriptable

Digging around a bit, apparently astroid thinks the headers returned
from call_app will always be None -- I guess it doesn't like our use of
a list to work around py2's lack of `nonlocal`.

By using a proper object to encapsulate state, we can shut up those
"error"s.

Also, pin upper-constraints to pike for keystone-related jobs.

Change-Id: I5ff21260872f4089b030cd94e494dc346ae74b8e

swift3/test/unit/__init__.py

@@ -118,14 +118,16 @@ class Swift3TestCase(unittest.TestCase):
 
         req.headers.setdefault("User-Agent", "Mozzarella Foxfire")
 
-        status = [None]
-        headers = [None]
+        class StartResponseContext(object):
+            status = headers = None
 
-        def start_response(s, h, ei=None):
-            status[0] = s
-            headers[0] = swob.HeaderKeyDict(h)
+            def __call__(self, s, h, ei=None):
+                self.status = s
+                self.headers = swob.HeaderKeyDict(h)
 
-        body_iter = app(req.environ, start_response)
+        sr = StartResponseContext()
+
+        body_iter = app(req.environ, sr)
         body = ''
         caught_exc = None
         try:
@@ -138,9 +140,9 @@ class Swift3TestCase(unittest.TestCase):
                 raise
 
         if expect_exception:
-            return status[0], headers[0], body, caught_exc
+            return sr.status, sr.headers, body, caught_exc
         else:
-            return status[0], headers[0], body
+            return sr.status, sr.headers, body
 
     def call_swift3(self, req, **kwargs):
         return self.call_app(req, app=self.swift3, **kwargs)

tox.ini

@@ -32,6 +32,7 @@ setenv = {[testenv]setenv}
 commands = /bin/bash {posargs:swift3/test/functional/run_test.sh}
 setenv = {[testenv]setenv}
          AUTH=keystone
+         UPPER_CONSTRAINTS_FILE=https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt?h=stable/pike
 # keystone 12.0.0 (pike) from openstack.org
 deps =
   {[testenv]deps}
@@ -63,8 +64,7 @@ setenv = {[testenv]setenv}
 
 [testenv:s3tests_keystone]
 commands = /bin/bash {posargs:swift3/test/functional/run_test.sh}
-setenv = {[testenv]setenv}
-         AUTH=keystone
+setenv = {[testenv:keystone]setenv}
          S3ACL=true
          DNS_BUCKET_NAMES=false
          CHECK_BUCKET_OWNER=true