ran python-modernize and isort on files mentioned in INCR-367

changes made to comply with pylint

openedx/core/djangoapps/credentials/admin.py

@@ -2,6 +2,8 @@
 Django admin pages for credentials support models.
 """
 
+from __future__ import absolute_import
+
 from config_models.admin import ConfigurationModelAdmin
 from django.contrib import admin
 

openedx/core/djangoapps/credentials/models.py

@@ -2,12 +2,14 @@
 Models for credentials support for the LMS and Studio.
 """
 
-from urlparse import urljoin
+from __future__ import absolute_import
 
+import six
 from config_models.models import ConfigurationModel
 from django.conf import settings
 from django.db import models
 from django.utils.translation import ugettext_lazy as _
+from six.moves.urllib.parse import urljoin  # pylint: disable=import-error
 
 from openedx.core.djangoapps.site_configuration import helpers
 
@@ -130,4 +132,4 @@ class NotifyCredentialsConfig(ConfigurationModel):
     )
 
     def __unicode__(self):
-        return unicode(self.arguments)
+        return six.text_type(self.arguments)

openedx/core/djangoapps/credentials/utils.py

 """Helper functions for working with Credentials."""
-from __future__ import unicode_literals
+from __future__ import absolute_import, unicode_literals
 
 from edx_rest_api_client.client import EdxRestApiClient