Improved ci/clean-build-package.sh for use on a new system

Check if things exist before trying to remove them.

Ticket: none
Changelog: none
(cherry picked from commit d8bac4d)

ci/clean-build-package.sh

@@ -3,6 +3,12 @@ set -ex
 # clean up docker stuff
 name=cfengine-build-package
 # TODO: a softer clean might get into the container and run ./buildscripts/build-scripts/clean-buildmachine
-docker stop $name
-docker rm -f $name
-docker rmi -f $name
+if docker ps | grep $name; then
+  docker stop $name
+fi
+if docker ps -a | grep $name; then
+  docker rm $name
+fi
+if docker images | grep $name; then
+  docker rmi -f $name
+fi