Enable colcon defaults file to customize list/build

[emersonknapp]

Description

It should be possible now to customize the colcon build with arbitrary arguments such as --packages-up-to by providing a colcon defaults file.

If the user can easily provide this, then we can avoid having to expose any explicit arguments.

Side effect, this should enable customization of colcon list for the rosdep collection step.

Related Issues

N/A

Completion Criteria

• User can pass arbitrary extra arguments to colcon build (build step) and colcon list (in rosdep gathering step)

Implementation Notes / Suggestions

Suggest a defaults.yaml file at root of workspace, and build_workspace.sh sets the COLCON_DEFAULTS_FILE or COLCON_HOME environment variable appropriately. See https://colcon.readthedocs.io/en/released/user/configuration.html#defaults-yaml

Testing Notes / Suggestions

Create test workspace with 2 packages with different dependencies. Run rosdep collection script with defaults file that specifies --packages-select one_package. Check output script for its dependencies.

Continue above experiment into build phase and check that build directory only contains the one package