docker_build: remove -f as the option flag does not exist anymore in 17.03.1 ce

docker_build

@@ -42,7 +42,7 @@
 for bookmark in $(cd $project_home && hg id -B);
 do
   echo "Docker tag with hg bookmark: $bookmark"
-  docker tag -f $registry/$image $registry/$image:$bookmark || { echo 'Tag failed' ; exit 1; }
+  docker tag $registry/$image $registry/$image:$bookmark || { echo 'Tag failed' ; exit 1; }
 done
 
 echo "Pushing docker image"