This commit fixes ros-simulation#612, but only for Gazebo9. Fixing it for Gazebo7
(the version used in ROS Kinetic) requires the following PR to be
backported to Gazebo 7 and 8:

https://bitbucket.org/osrf/gazebo/pull-requests/2814/fix-issue-2111-by-providing-options-to/diff

Once that PR has been backported, we can remove the GAZEBO_MAJOR_VERSION
guards from this PR so that the fix is active for the older Gazebo
versions as well.

Tested on Gazebo7 (where it compiles, but doesn't change anything) and
Gazebo9 (where it compiles and fixes the bug). I've tested it using the
instructions I've put into this repo:

https://github.com/mintar/mimic_joint_gazebo_tutorial