disable tests with clang
disable tests with clang

qt5 tests with clang are broken on travis, we would need Qt >= 5.1.1
due to the following bug:

https://bugreports.qt-project.org/browse/QTBUG-32100

gamenet/qxmpp,Kaffeine/qxmpp,kollix/qxmpp,gotomypc/qxmpp,gotomypc/qxmpp,ycsoft/qxmpp,deepak899/qxmpp,gamenet/qxmpp,Kaffeine/qxmpp,olesalscheider/qxmpp,LightZam/qxmpp,olesalscheider/qxmpp,Kaffeine/qxmpp,Ilyatk/qxmpp,kollix/qxmpp,cccco/qxmpp,KangLin/qxmpp,pol51/QXMPP-CMake,deepak899/qxmpp,gotomypc/qxmpp,gamenet/qxmpp,Ilyatk/qxmpp,cccco/qxmpp,ycsoft/qxmpp,Ilyatk/qxmpp,kollix/qxmpp,KangLin/qxmpp,KangLin/qxmpp,deepak899/qxmpp,LightZam/qxmpp,cccco/qxmpp,ycsoft/qxmpp,pol51/QXMPP-CMake,LightZam/qxmpp,olesalscheider/qxmpp,pol51/QXMPP-CMake