SlicerCochlea: Cdash test keeps failing

Site Name: metroplex.kitware
Build Name: 27501-SlicerCochlea-git722d991-g+±64bits-Qt5.11-Release
Stamp: 20181209-0300-Extensions-4.10-Nightly
Time: 2018-12-09T05:37:17 UTC
Type: Extensions-4.10-Nightly
OS Name: Linux
OS Platform: x86_64
OS Release: 3.10.0-514.6.1.el7.x86_64
OS Version: #1 SMP Sat Dec 10 11:15:38 EST 2016
CTest version: ctest-3.12.1
Test output

 qt.qpa.screen: QXcbConnection: Could not connect to display :0 Could not connect to any X display.

What does this error mean?

Here is the link.

This is a configuration issue on the build&test server: display is not configured correctly.

@jcfr could you have a look? Thanks!