[build.kde.org] Verbose output for the tests failures

[Christophe Giboudeaux]

Hello,

A couple days ago, Ben pushed a tiny change [1] to the build.kde.org config 
files.
Now, when a test fails on the CI, il will also paste the test output instead 
of just mentioning 'test xx failed'.

This should hopefully help finding why some tests succeed locally but fail on 
build.kde.org.

Note that due to a docker limitation, ctest cannot get a backtrace when a test 
crashes.

GDB needs certain capabilities in order to generate backtraces, which by 
default, Docker restricts.
Some of these restrictions can be disabled when creating the docker image but 
the Jenkins plugin we use for interfacing with Docker does not have support 
for utilising that part of Docker's API [2]

(Thanks Ben for the extra information)

[1] https://phabricator.kde.org/R857:a8987860f719cf53dec44f2ff776ff1a013ec1c2
[2] See https://phabricator.kde.org/T5460 for more information