Split the setcap image from the base images, make them easier to override

build/server-image/Dockerfile

@@ -14,10 +14,9 @@
 
 # Dockerfile used for the server images.
 
-ARG BASE_IMAGE_REGISTRY
-ARG BASE_IMAGE_NAME
+ARG BASEIMAGE
 ARG BINARY
 
 
-FROM "${BASE_IMAGE_REGISTRY}/${BASE_IMAGE_NAME}"
+FROM "${BASEIMAGE}"
 COPY ${BINARY} /usr/local/bin/${BINARY}