Evaluate filter() generator before returning in get_param_names()

[stevegolton]

See issue #527.

This patch was needed when running rosapi under ROS Noetic which uses python3 due to the difference in in the return type of the filter() function between python2 and python3. In python2, a list is returned directly, but in python 3 a generator is returned which needs to be evaluated into a list to match the expected return type of the get_param_names() function in params.py.

Also tested using the ros-melodic docker container which uses python2 and it seems to work fine.

Please let me know if this is the wrong place to submit pull requests to, or if the python3/noetic migration work is being done elsewhere?

[mvollrath]

This is a good place for it, we've been keeping Python 2/3 compatibility in noetic.

It looks like the tests are choking on some ROS test infrastructure, maybe something in here, but I don't see an issue tracked yet.

[mvollrath]

Tests are passing for me.

[stevegolton]

Thanks @mvollrath! I was struggling a little with those tests.