Extend workspace packages using ament index for ROS2 support

[ruffsl]

Fixes #660

[codecov-io]

Codecov Report

Merging #699 into master will increase coverage by 0.29%.
The diff coverage is 95.55%.

@@            Coverage Diff             @@
##           master     #699      +/-   ##
==========================================
+ Coverage   75.47%   75.77%   +0.29%     
==========================================
  Files          32       37       +5     
  Lines        2968     3013      +45     
==========================================
+ Hits         2240     2283      +43     
- Misses        728      730       +2

Impacted Files	Coverage Δ
src/rosdep2/ament_packages/packages.py	100% <100%> (ø)
src/rosdep2/ament_packages/constants.py	100% <100%> (ø)
src/rosdep2/ament_packages/resources.py	100% <100%> (ø)
src/rosdep2/ament_packages/__init__.py	100% <100%> (ø)
src/rosdep2/ament_packages/search_paths.py	87.5% <87.5%> (ø)
src/rosdep2/main.py	49.35% <90%> (+0.76%)	⬆️
... and 1 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ab1f06e...a52f89f. Read the comment docs.

[wjwwood]

Copying the code sucks, but I guess it's unavoidable right now. However, please make a comment (or a README.md in the ament_packages folder) mentioning that this code is essentially copied directly from ament_package or ament_index_python or wherever it came from. That way it can be more easily updated in the future.

I think at least one test would be a good idea, and maybe one for the case I mentioned in my comment (mixing ROS 1 and ament packages).

[ruffsl]

@wjwwood , I've added the readme linking to the repo/commit copied from, as well a extension to the install tests to check the behavior when colliding packages from ament and package path.

[ruffsl]

While testing this branch in the wild, I found the ament_packages sub module wasn't being installed. I've updated the setup.py to fix this and can confirm this patch is working as expected. See this before, after Dockerfile that achieve the same effect, now without needing to monkeypatch ROS_PACKAGE_PATH everyware: ros-swg/turtlebot3_demo@97d9c33

Could we merge this upstream for the next eventual sync?

[ruffsl]

I'll be triggering an update to the ros docker image library soon. I would be neat to have this included.
bump @wjwwood @dirk-thomas .

[wjwwood]

Makes sense to me.

[wjwwood]

I'll try to merge and release this asap, but I can't do it today.

[ruffsl]

@wjwwood , now that dashing sync is out, I'd like to get this in the docker library rebuild as well.
Please ping back when ready so that I can open the PR upstream.

[wjwwood]

Looks like either I will release this next week (I'm pretty busy for the rest of this week), or maybe @nuclearsandwich because I think he mentioned on discourse he may do a release soon.