tests: Fix auth tests

Hongliang Wang made a couple of suggestions regarding the recently
merged auth tests:

 - Authentication failure should return code 401, not 403.
 - Removing the '{}' return from the login REST API broke the UI

This patch addresses both of these comments.

Cc: Hongliang Wang <hlwang@linux.vnet.ibm.com>
Signed-off-by: Adam Litke <agl@linux.vnet.ibm.com>
Fix Log-in Window Redrawn after 401 Returned

Log-in window will be cleared and re-drawn after 401 returned when
username/password is wrong. This will cause message like "username
or password is incorrect." disappear. It's because login() is also
be filtered for 401 using kimchi.requestJSON() that is intended to
filter Ajax requests for RESTful APIs after the user has logged in
successfully. In this patch, we'll use jQuery.ajax() for login().

Signed-off-by: Hongliang Wang <hlwang@linux.vnet.ibm.com>