Fix password not strong enough failures

Use rand_password method to create users with more complex
passwords.

Closes-Bug: 1448217
Depends-On: I86bf157f1bdb44f5fc579dc5317784fe31df8521
Change-Id: I57649f5aac9b1abe1a9961d4b35479372ebee519
diff --git a/tempest/api/identity/admin/v3/test_groups.py b/tempest/api/identity/admin/v3/test_groups.py
index 260ea54..e022023 100644
--- a/tempest/api/identity/admin/v3/test_groups.py
+++ b/tempest/api/identity/admin/v3/test_groups.py
@@ -67,7 +67,8 @@
         users = []
         for i in range(3):
             name = data_utils.rand_name('User')
-            user = self.client.create_user(name)['user']
+            password = data_utils.rand_password()
+            user = self.client.create_user(name, password)['user']
             users.append(user)
             self.addCleanup(self.client.delete_user, user['id'])
             self.groups_client.add_group_user(group['id'], user['id'])