ign-gazebo3 DiffDriveTest.SkidPublishCmd test failing

https://build.osrfoundation.org/job/ignition_gazebo-ci-ign-gazebo3-bionic-amd64/55/testReport/

```
/var/lib/jenkins/workspace/ignition_gazebo-ci-ign-gazebo3-bionic-amd64/ign-gazebo/test/integration/diff_drive_system.cc:306
Expected: (poses[0].Pos().Y()) < (poses[3999].Pos().Y()), actual: 2 vs 2
```