Option to exclude files from ament_auto_lint

[jacobperron]

It would be convenient if there was a way to exclude one or more files from lint checks when invoking ament_auto_lint.
This would be useful in circumstances were a package includes third-party source files (e.g. tinydir in ros2/rcl#332).
Currently, there is no apparent way to exclude a file other than not running a particular lint check.
Linters could be called separately (ie. not with ament_auto_lint), but some would still need to be extended to support file exclusions.

Implementation considerations

Ideally, we could pass a file exclusion list to ament_auto_lint and let it pass the appropriate flags to the linters it invokes, e.g.

ament_lint_auto_find_test_dependencies(
  EXCLUDE_FILES
    include/foo/bar.h
    src/bar.c
    src/baz.c
)

Another option could be to support placing a file (e.g. ament_lint.cfg) in the root of the repo that allows configuration of the various linters supported by ament_lint.

[jacobperron]

cc/ @AAlon

[emersonknapp]

I believe this was closed with #386

[methylDragon]

This issue was also duplicated in #343

I think I will close this.

---

To exclude files, simply:

    # this must happen before the invocation of ament_package()
    if(BUILD_TESTING)
      find_package(ament_lint_auto REQUIRED)
      set(AMENT_LINT_AUTO_FILE_EXCLUDE /path/to/ignored_file ...)
      ament_lint_auto_find_test_dependencies()
    endif()