Copy cv2 into virtualenv

.travis.yml

@@ -49,8 +49,6 @@ sudo: required
 group: edge
 language: python
 python: "2.7.14"
-virtualenv:
-  system_site_packages: true
 cache:
   - apt
 
@@ -106,6 +104,7 @@ before_script:
   # package depdencies: install using rosdep.
   - cd ~/catkin_ws
   - rosdep install -y --from-paths src --ignore-src --rosdistro $ROS_DISTRO
+  - cp /usr/lib/python2.7/dist-packages/cv2.so $VIRTUAL_ENV/lib/python2.7/site-packages/
 
 # Compile and test (mark the build as failed if any step fails). If the
 # CATKIN_OPTIONS file exists, use it as an argument to catkin_make, for example