Running a node that uses gazebo using docker exec doesn't work

[princebansal]

After I run the container using docker run -d -p 5901:5901 -p 6901:6901 henry2423/ros-vnc-ubuntu:kinetic, I can access the vnc interface through my browser.
Now I have a sample project rrbot https://github.com/ros-simulation/gazebo_ros_demos.
I can only start the gazebo when I run the roslaunch command from browser.
But if I run the roslaunch command using docker exec -t c32f456bba2c bash -c "roslaunch rrbot_gazebo rrbot_world.launch", it starts the node but doesn't spin up gazebo in the vnc desktop. It gets stuck here

started core service [/rosout]
process[gazebo-2]: started with pid [176]
[ INFO] [1600019161.652547400]: Finished loading Gazebo ROS API Plugin.
[ INFO] [1600019161.653956700]: waitForService: Service [/gazebo/set_physics_properties] has not been advertised, waiting...
process[gazebo_gui-3]: started with pid [196]
[ INFO] [1600019162.131817800]: Finished loading Gazebo ROS API Plugin.
[ INFO] [1600019162.132983500]: waitForService: Service [/gazebo/set_physics_properties] has not been advertised, waiting...
gazeb: cannot connect to X server 
terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::lock_error> >'
terminate called recursively
  what():  boost: mutex lock failed in pthread_mutex_lock: Invalid argument
Aborted
process[urdf_spawner-4]: started with pid [278]
[gazebo_gui-3] process has died [pid 196, exit code 134, cmd /opt/ros/kinetic/lib/gazebo_ros/gzclient __name:=gazebo_gui __log:=/home/ubuntu/.ros/log/fbc04204-f5e8-11ea-b56f-0242ac110002/gazebo_gui-3.log].
log file: /home/ubuntu/.ros/log/fbc04204-f5e8-11ea-b56f-0242ac110002/gazebo_gui-3*.log
SpawnModel script started
[INFO] [1600019162.889144, 0.000000]: Loading model XML from ros parameter
[INFO] [1600019162.892796, 0.000000]: Waiting for service /gazebo/spawn_urdf_model

Can you please help?