v2: Content-Type: application/octet-stream header always added

The bug: any existing Content-Type header cannot be found because the
call to headers.get() fails. Therefore we end up with two Content-Type
headers because a new one (applicaion/octet-stream) gets added
unconditionally. The cause: the strings (keys and values) in the headers
dict are converted from unicode sequences of type <str> to utf-8
sequences of type <bytes>. This happens in safe_encode()
(oslo_utils/encodeutils.py:66). <str> != <bytes> even if they appear to
have the same characters.

Hence, for python 3.x, _set_common_request_kwargs() adds content-type
to header even if custom content-type is set in the request.

This results in unsupported media type exception when glance client
is used with keystoneauth and python 3.x

The fix: follow the directions in encode_headers().
It says to do this just before sending the request. Honor this principle;
do not encode headers and then perform more business logic on them.

Change-Id: Idf6079b32f70bc171f5016467048e917d42f296d
Closes-bug: #1641239
Co-Authored-By: Pushkar Umaranikar <pushkar.umaranikar@intel.com>

glanceclient/tests/functional/base.py

@@ -10,8 +10,10 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import glanceclient
+from keystoneauth1 import loading
+from keystoneauth1 import session
 import os
-
 import os_client_config
 from tempest.lib.cli import base
 
@@ -60,3 +62,30 @@ class ClientTestBase(base.ClientTestBase):
     def glance(self, *args, **kwargs):
         return self.clients.glance(*args,
                                    **kwargs)
+
+    def glance_pyclient(self):
+        ks_creds = dict(
+            auth_url=self.creds["auth_url"],
+            username=self.creds["username"],
+            password=self.creds["password"],
+            project_name=self.creds["project_name"])
+        keystoneclient = self.Keystone(**ks_creds)
+        return self.Glance(keystoneclient)
+
+    class Keystone(object):
+        def __init__(self, **kwargs):
+            loader = loading.get_plugin_loader("password")
+            auth = loader.load_from_options(**kwargs)
+            self.session = session.Session(auth=auth)
+
+    class Glance(object):
+        def __init__(self, keystone, version="2"):
+            self.glance = glanceclient.Client(
+                version,
+                session=keystone.session)
+
+        def find(self, image_name):
+            for image in self.glance.images.list():
+                if image.name == image_name:
+                    return image
+            return None