Creating a new user with an existing user name

Change error message when we create a new user
with an existing user name.

Change-Id: I795c04672a3c625be074c8af78eb169436ac3895
Closes-Bug: #1404432
Imported Translations from Transifex

For more information about this automatic import see:
https://wiki.openstack.org/wiki/Translations/Infrastructure

Change-Id: I3a6a78cc5747c1f0f7dd1cd9d6a311705e6ad964
Merge "Creating a new user with an existing user name"