Take advantage of variable substitution already in the Makefile to specify the correct location for files in init.d.

(closes issue #16979)
 Reported by: jw-asterisk
 
(issue #15691)
 Reported by: itamarjp


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@268534 65c4cc65-6c06-0410-ace0-fbb531ad65f3