packaging: fix deb 8 being built on deb 9

Dockerfile must ask for 'jessie', otherwise it downloads
'stretch' even though 8 is jessie and 9 is stretch.

Issue: #81456
Change-Id: I2ee41b85de8a2a1e76a89c29602a4f94500729c4

docker/debian_8/Dockerfile

-FROM debian:8
+FROM debian:jessie
 
 RUN apt-get update && ( apt-get upgrade -y || apt-get upgrade -y || apt-get upgrade -y )
 RUN apt-get install -y devscripts debianutils debhelper build-essential tar \