add frame_id and child_frame_id attribute support for DiffDrive

[doisyg]

Add configuration of the odom frame_id and child_frame_id fields from sdf attributes <frame_id> and <child_frame_id>
Example:

    <plugin
      filename="libignition-gazebo-diff-drive-system.so"
      name="ignition::gazebo::systems::DiffDrive">
      <left_joint>left_wheel_joint</left_joint>
      <right_joint>right_wheel_joint</right_joint>
      <wheel_separation>${base_y_origin_to_wheel_origin*2}</wheel_separation>
      <wheel_radius>${wheel_radius}</wheel_radius>
      <odom_publish_frequency>20</odom_publish_frequency>
      <topic>cmd_vel</topic>
      <odom_topic>odom</odom_topic>
      <frame_id>odom</frame_id>
      <child_frame_id>base_footprint</child_frame_id>
    </plugin>

Partialy solves #340

[azeey]

Thank you for the contribution! The changes all look good to me. I left a couple nitpick comments. One last think I would ask is if you could add a test checking if both the old and new behaviors work as expected. The best place to add it would be in test/integration/diff_drive_system.cc

[doisyg]

One last think I would ask is if you could add a test checking if both the old and new behaviors work as expected. The best place to add it would be in test/integration/diff_drive_system.cc

Can you point me to a documentation on how to write/use these tests ?

[chapulina]

Can you point me to a documentation on how to write/use these tests ?

It's on the README:

https://github.com/ignitionrobotics/ign-gazebo#testing

If you're using colcon, you can run colcon test.

Our high-level contribution docs also have more info:

https://ignitionrobotics.org/docs/all/contributing#writing-tests

[doisyg]

Synced and added 2 tests for old and new behaviors.
Sorry about the delay

[azeey]

Thanks for adding the tests. I have left some fairly minor comments that I think would simplify the tests. I would also ask if you could fix some code style issues according to our style guide. You can find the errors in the github build, but you can also check locally by running make codecheck.

Otherwise, this looks pretty good.

[doisyg]

Hopefully more simple tests and better style

[azeey]

I have one more style nit. Also, could you signing off on your commits? Here are the instructions:
https://github.com/ignitionrobotics/ign-gazebo/pull/361/checks?check_run_id=1494209342

[azeey]

The test failures are not caused by this PR, so I'm ready to merge. I think the only thing left is the DCO.

[azeey]

I think there was a bad merge/rebase. This now shows conflicts in files not touched by this PR. Do you mind rebasing on to ign-gazebo3 without including commits outside of this PR? If you have the https://github.com/ignitionrobotics/ign-gazebo/ as upstream, you can do:

# With the PR branch checked out
git fetch upstream

git rebase -i --signoff upstream/ign-gazebo3
# drop commit d353f66b
git push --force-with-lease

[doisyg]

Done, sorry about the mess caused by the signofff/rebase

[azeey]

Thanks for getting the DCO issue resolved. I have a couple more requests that should help with the failing tests.

[azeey]

Looks like there are still some failures. I think merging from ign-gazebo3 would fix them though. If you don't mind giving me write permission to the PR, I can do it for you.

[doisyg]

Looks like there are still some failures. I think merging from ign-gazebo3 would fix them though. If you don't mind giving me write permission to the PR, I can do it for you.

For some reason, I could not find the option to give you a write permission. Indeed the codecheck failure are not related to this PR. I merged ign-gazebo3 into this PR branch

[azeey]

LGTM! The remaining test failures appear to be flaky or unrelated to this PR. Thanks for your patience.