much faster rebuild of docker image

Change-Id: Icd2f8462e301c219a625897f0f7cfb85094f6c04
diff --git a/mwc-bpr-docker.sh b/mwc-bpr-docker.sh
index e83febe..395053f 100755
--- a/mwc-bpr-docker.sh
+++ b/mwc-bpr-docker.sh
@@ -4,8 +4,9 @@
 
 set -ex
 
-docker build -t onos-fabric-mwc .
+$ONOS_ROOT/tools/build/onos-buck build onos
+docker build -f Dockerfile.prebuilt -t onos-fabric-mwc .
 docker tag onos-fabric-mwc 10.128.13.3:5000/onosproject/onos:candidate
 docker push 10.128.13.3:5000/onosproject/onos:candidate
 
-ssh head "cd /opt/onos_fabric/ && docker-compose down && docker-compose pull && docker-compose up -d"
+# ssh head "cd /opt/onos_fabric/ && docker-compose down && docker-compose pull && docker-compose up -d"