Use custom buildkit and rm worker

.drone.yml

@@ -15,13 +15,15 @@ steps:
           path: /var/run/docker.sock
     commands:
         - docker run --rm --privileged docker/binfmt:a7996909642ee92942dcd6cff44b9b95f08dad64
-        - docker buildx create --use --name crosscomp
+        - export BUILDER_ID="crosscomp-$(cat /proc/self/cgroup | head -1 | cut -d '/' -f 3)"
+        - docker buildx create --use --name $BUILDER_ID --driver-opt image=stargate01/buildkit
         - docker buildx inspect --bootstrap
         - docker login --username $DOCKER_USERNAME --password $DOCKER_PASSWORD registry.chrz.de
         - docker buildx build --platform linux/amd64,linux/arm/v7 --output=type=image,push=true --progress tty 
             --build-arg PROP_SERVER --build-arg PROP_SERVER_USER 
             --build-arg PROP_SERVER_KEY --build-arg PROP_DIR_SDR --build-arg PROP_DIR_DECODER 
             -t registry.chrz.de/redsat/move2docker .
+        - docker buildx rm $BUILDER_ID
     environment:
         PROP_SERVER_USER:
             from_secret: prop_server_user