GLX extension is disabled on docker on travis

Current test on docker on travis may fails because of no GLX extension.

Confirmed on my fork https://travis-ci.org/furushchev/jsk_robot/jobs/199456288 The test itself succeeded but shows at log:

Loading extension GLX
(EE) 
Fatal server error:
(EE) no screens found(EE) 
(EE) 
Please consult the The X.Org Foundation support 
     at http://wiki.x.org
 for help. 
(EE) Please also check the log file at "/tmp/xorg.log" for additional information.
(EE) 
(EE) Server terminated with error (1). Closing log file.
+ glxinfo
+ grep GLX
Error: unable to open display :0

and

Gazebo multi-robot simulator, version 2.2.3
Copyright (C) 2012-2014 Open Source Robotics Foundation.
Released under the Apache 2 License.
http://gazebosim.org

Gazebo multi-robot simulator, version 2.2.3
Copyright (C) 2012-2014 Open Source Robotics Foundation.
Released under the Apache 2 License.
http://gazebosim.org

.[ INFO] [1486518202.412394659]: Loading nodelet /head_camera/crop_decimate of type image_proc/crop_decimate to manager /head_camera/head_camera_nodelet_manager with the following remappings:
[ INFO] [1486518202.412488895]: /head_camera/camera/camera_info -> /head_camera/depth_registered/camera_info
[ INFO] [1486518202.412517188]: /head_camera/camera/image_raw -> /head_camera/depth_registered/image_raw
[ INFO] [1486518202.412537164]: /head_camera/camera_out -> /head_camera/depth_downsample
[ INFO] [1486518202.444633706]: waitForService: Service [/head_camera/head_camera_nodelet_manager/load_nodelet] has not been advertised, waiting...
[ INFO] [1486518202.600244129]: Finished loading Gazebo ROS API Plugin.

Msg Waiting for masterMsg Waiting for masterMsg Connected to gazebo master @ http://127.0.0.1:11345
Msg Publicized address: 172.17.0.2
Error [RenderEngine.cc:665] Can't open display: :0

gazebo rendering is disabled.

jsk-ros-pkg / jsk_travis

GLX extension is disabled on docker on travis #320