Code review comment for ~smoser/curtin:cleanup/fix-tip-pycodestyle-invalid-escape-sequences

IIRC, if we want to use \ escapes, then the string must be a raw string. There are few cases where you drop the r'' and others were you add it.

At least for regex, I think we can consistently use r'', and for other causes (we pass strings to a shell) we've escaped things like $; those, IIRC, don't need escaping unless we're running them through shell.