Fix regression: Sanitize sudo success_key from stdout

Commit 7e3dd10 caused a regression with sanitizing the sudo success_key from stdout.
There is no newline in front of SUDO-SUCCESS when using sudo.
This change adapts the regex to make the line break optional.

Tested on Ubuntu 14.04.
Merge branch 'patch-1' of https://github.com/debfx/ansible into debfx-patch-1
Merge branch 'debfx-patch-1' into devel