Add support to daemon-util for distributions without start-stop-daemon

This adds support to daemon-util for Red Hat based distributions that
do not have a start-stop-daemon. If /sbin/start-stop-daemon is not
available, daemon-util will source /etc/rc.d/init.d/functions.
check(), start(), and stop() are updated to use the relevant functions
from /etc/rc.d/init.d/functions.

Thanks to Stephen Fromm and Michael Hanselmann for improving the error
handling, style, and comments.

Signed-off-by: Jun Futagawa <jfut@integ.jp>
Reviewed-by: Michael Hanselmann <hansmi@google.com>