* Update travis to use ubuntu 16.04 (xenial)
Update travis to use ubuntu 16.04 (xenial) instead of 14.04 (trusty)
* add xvfb as a service to xenial distribution
* removed explicit start of xvfb
after adding the xvfb as a service, there is no reason to explicitly start it at "before_install"
* install libGL during before_install
* install libgl1-mesa-dev during "before_install"
After some changes from the Qt installers (? maybe), all Travis Android builds are not able to be configured in order to run.
Deactivating thier build till it get fixed.
Nikolaos Ftylitakis
KangLin