Docker: re-added post_push so that additional tags are pushed with automated build

docker/artful/hooks/post_push

@@ -0,0 +1,2 @@
+#!/bin/bash 
+docker push $DOCKER_REPO:17.10

docker/bionic/hooks/post_push

@@ -0,0 +1,2 @@
+#!/bin/bash 
+docker push $DOCKER_REPO:18.04

docker/xenial/hooks/post_push

@@ -0,0 +1,3 @@
+#!/bin/bash 
+docker push $DOCKER_REPO:16.04
+docker push $DOCKER_REPO:latest

docker/zesty/hooks/post_push

@@ -0,0 +1,2 @@
+#!/bin/bash 
+docker push $DOCKER_REPO:17.04