pip 10 gives exit code 1 for empty argument lists (pip < 10 gave exit 0)
see also https://github.com/pypa/pip/pull/4210
To still allow playbooks to pass when giving empty lists, don't call
pip in that case, but show a warning.
* Fix the editable condition into pip module (#19028)
* Add editable to tests
Default changed to False, so now editable: True is needed explicitly in
tests
This change corrects problems reported by the `yamllint` linter.
Since key duplication problems were removed in 4d48711, this commit
mainly fixes trailing spaces and extra empty lines at beginning/end of
files.
