Unclear message while renaming a user name with an existing user name

[Kanchan Gupta]

If we try to rename a user with existing user name then it shows unclear error message.

Current message is "Danger: There was an error submitting the form. Please try again"

Expected results : Should show the proper error message like "User with <user_name> already exists, Please try again."

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/133953

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/133953
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=95db4eb70912200986e71ec565a7bd7b02b626d5
Submitter: Jenkins
Branch: master

commit 95db4eb70912200986e71ec565a7bd7b02b626d5
Author: Vlad Okhrimenko <email address hidden>
Date: Wed Nov 12 15:25:30 2014 +0200

    Renaming a user name with an existing user name

    Change error message when we try rename user
    name with an existing user name.

    Change-Id: I2dbf9fee3c682a70c77544a8dd6b925311a3f019
    Closes-Bug: #1389132