Add an init script

This is a straight adaption of the salt-master init script (plus my recent
patch to it in holmboe/salt@464ca9dd1f86a4c686a56a6683dc412b67584f1c).
Fix the LSB header

I got complaints from insserv that the LSB header was not compliant. It was
missing required keywords, which must be there even if they are empty.
Merge pull request #42 from holmboe/init-script

Add an init script