Replace hardcoded admin url with reverse()

The admin change view URL changes in django 1.9 and it's good practice
to use reserve() anyway.

coin/members/tests.py

@@ -16,6 +16,7 @@ from django.conf import settings
 from django.test import TestCase, Client
 from django.core import mail, management
 from django.core.exceptions import ValidationError
+from django.core.urlresolvers import reverse
 
 from coin.members.models import Member, MembershipFee, LdapUser
 from coin.offers.models import OfferSubscription, Offer
@@ -426,7 +427,9 @@ class MemberAdminTests(TestCase):
                         last_name=last_name, username=username)
         member.save()
 
-        edit_page = self.client.get('/admin/members/member/%i/' % member.id)
+        edit_page = self.client.get(reverse('admin:members_member_change',
+                                            args=(member.id,)))
+
         self.assertNotContains(edit_page,
                                '''<input id="id_username" />''',
                                html=True)