It is a permission "problem", not a bug. The only issue is that user is not informed through the gui.
Please attach the debug log (it would be different than the one from the bug 1377100 due to dependencies)
Thanks
I verified it with virt-viewer-2.0-17.el6.x86_64.
Configure a vnc unix guest, then connect to it by normal user.
$ virt-viewer -c qemu:///system testvnc
And error dialog "Failed to connect: Connecting to unix socket failed: Permission denied" pops.
So move the bug from ON_QA to VERIFIED.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://rhn.redhat.com/errata/RHBA-2017-0587.html