createsuperuser doesn't accept default username
|Reported by:||Russell Keith-Magee||Owned by:||nobody|
|Has patch:||no||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
The createsuperuser command prompts for a username, saying '(leave blank to use u'rkm')".
However, after the merge of the #3011 changes, a blank username is rejected as invalid input.
Also, the prompt shouldn't include the u prefix.