Update to double-dash everywhere

These were found using `git grep -nE '[^-a-zA-Z0-9<>]-[a-zA-Z0-9]{2}'` (fair warning: _many_ false positives there).

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #4646 from tianon/double-dash

Update to double-dash everywhere