Check if the group exists

When setting default group, we should check if the group exists.
If not, it could lead to some issues with adding new users after
the new default group is set.

https://fedorahosted.org/freeipa/ticket/504

ipalib/plugins/config.py

@@ -149,6 +149,12 @@ class config_mod(LDAPUpdate):
                 entry_attrs['ipamigrationenabled'] = 'TRUE'
             else:
                 entry_attrs['ipamigrationenabled'] = 'FALSE'
+        if 'ipadefaultprimarygroup' in entry_attrs:
+            group=entry_attrs['ipadefaultprimarygroup']
+            try:
+                api.Command['group_show'](group)
+            except errors.NotFound:
+                raise errors.NotFound(message=unicode("The group doesn't exist"))
         return dn
 
 api.register(config_mod)