Small fixes for WebOb 1.7 compatibiltity

WebOb 1.7 includes a few changes that are not backward
compatible. The ones I noticed and fixed are:
 1. When supplying unicode content for the response body
    the charset is now required if headers are also provided.
    Previously a default was used.
 2. Content-Length is no longer being set when creating a
    webob.Response object. It appears to be correctly set
    when directly setting the body property.

Upstream change that caused the issues:
  https://github.com/Pylons/webob/commit/35fd585

Closes-bug: #1657452
Change-Id: Iaf2dd45fc86e3eb5e56be0a3e1582a6ddf960bc1

keystone/federation/controllers.py

@@ -353,7 +353,7 @@ class Auth(auth_controllers.Auth):
 
         subs = {'host': host, 'token': token_id}
         body = src.substitute(subs)
-        return webob.Response(body=body, status='200',
+        return webob.Response(body=body, status='200', charset='utf-8',
                               headerlist=headers)
 
     def _create_base_saml_assertion(self, context, auth):

keystone/tests/unit/test_wsgi.py

@@ -164,7 +164,6 @@ class ApplicationTest(BaseWSGITest):
             headers=[('Byte-Header', 'Byte-Value'),
                      (u'Unicode-Header', u'Unicode-Value')])
         # assert that all headers are identified.
-        self.assertThat(resp.headers, matchers.HasLength(4))
         self.assertEqual('Unicode-Value', resp.headers.get('Unicode-Header'))
         # assert that unicode value is converted, the expected type is str
         # on both python2 and python3.
@@ -176,7 +175,6 @@ class ApplicationTest(BaseWSGITest):
         self.assertEqual('204 No Content', resp.status)
         self.assertEqual(http_client.NO_CONTENT, resp.status_int)
         self.assertEqual(b'', resp.body)
-        self.assertEqual('0', resp.headers.get('Content-Length'))
         self.assertIsNone(resp.headers.get('Content-Type'))
 
     def test_render_response_head_with_body(self):