lib/tools/ensure_dirs.py: Code formatting

Wrap lines in a consistent manner (uid/gid on the second line) if
wrapping is necessary at all. “git diff --color-words” shows no
difference at all as only whitespace changed.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>