Filter the init script name parameter through fs.basename() to avoid
invoking paths outside of /etc/init.d/.
Reported-by: Graham R <gr348@cam.ac.uk>
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit 8752701b0d01a81d0bd0a735be733f24ad11ab69)