webadmin: Fix error message on change DC quota mode

When creating a new DC and changing the DC Quota enforcement mode to
Audit, no message should be presented.

Fixed logic of the message pop up

Change-Id: I21e4238979c225b2c6a2a04702c73b50f5c4e8b4
Bug-Url: https://bugzilla.redhat.com/974172
Signed-off-by: Ofri Masad <omasad@redhat.com>