Add sysv support to elements/dhcp-all-interfaces

This patch adds support for sysv init to the dhcp-all-interfaces element.
Specifically, it adds a sysv init script and the relevant install/config steps.

Tested with Debian jessie/testing.

Change-Id: I4ae1d5365bafda188cb65ea1fb72d8ffe2408910
Merge "Add sysv support to elements/dhcp-all-interfaces"