Introduce BASEIMAGE ARG to avoid redundant dockerfiles

Both oneapi_jug_xl and jug_xl are built from the same
containers/jug/xl.Dockerfile with the base image changed using
build args

.gitlab-ci.yml

@@ -272,7 +272,7 @@ oneapi_jug_xl:default:
   script:
     - cp containers/jug/setup_detectors.py containers/oneapi
     - cp detectors.yaml containers/oneapi
-    -  docker build -t ${CI_REGISTRY_IMAGE}/${BUILD_IMAGE}:${INTERNAL_TAG} 
+    - docker build -t ${CI_REGISTRY_IMAGE}/${BUILD_IMAGE}:${INTERNAL_TAG} 
                    -f containers/jug/xl.Dockerfile 
                    --build-arg INTERNAL_TAG=${INTERNAL_TAG}
                    --build-arg BASEIMAGE="oneapi_jug_dev"
@@ -300,10 +300,11 @@ oneapi_jug_xl:nightly:
     BUILD_IMAGE: "oneapi_jug_xl"
   script:
     - cp containers/jug/setup_detectors.py containers/oneapi
-    - cp detectors.yaml containers/oneapi
-    - sed 's/^FROM.*$/FROM ${DOCKER_REGISTRY}oneapi_jug_dev:${INTERNAL_TAG}/' containers/jug/xl.Dockerfile |  
-      docker build \- -t ${CI_REGISTRY_IMAGE}/${BUILD_IMAGE}:${NIGHTLY_TAG}
+    - cp detectors.yaml containers/oneapi 
+    - docker build -t ${CI_REGISTRY_IMAGE}/${BUILD_IMAGE}:${NIGHTLY_TAG}
+                   -f containers/jug/xl.Dockerfile 
                    --build-arg INTERNAL_TAG=${INTERNAL_TAG}
+                   --build-arg BASEIMAGE="oneapi_jug_dev"
                    --build-arg JUG_VERSION=nightly-$(date +%Y-%m-%d_%H-%M-%S)-${INTERNAL_TAG}-$(git rev-parse HEAD)
                    --build-arg NIGHTLY=1
                     containers/oneapi

containers/jug/xl.Dockerfile

 #syntax=docker/dockerfile:1.2
 ARG DOCKER_REGISTRY="eicweb.phy.anl.gov:4567/containers/eic_container/"
-ARG INTERNAL_TAG="testing" 
+ARG INTERNAL_TAG="testing"
+ARG BASEIMAGE="jug_dev"
 
 ## ========================================================================================
 ## STAGE1: spack builder image
 ## EIC builder image with spack
 ## ========================================================================================
-FROM ${DOCKER_REGISTRY}jug_dev:${INTERNAL_TAG}
+FROM ${DOCKER_REGISTRY}${BASEIMAGE}:${INTERNAL_TAG}
 
 ARG EICWEB="https://eicweb.phy.anl.gov/api/v4/projects"
 ARG JUGGLER_VERSION="master"