rhbz1007106 - Correct error when signing up with open where the open id username is the same as an existing Zanata user name.

Also remove some default values for username and email when using open id as they might be invalid.
Merge pull request #178 from zanata/rhbz1007106

rhbz1007106 - Correct error when signing up with open where the open id username is the same as an existing Zanata user name.