[Infra] Re-use build extra env vars to enable no cache option

Author: auphelia

run-docker.sh

@@ -192,17 +192,15 @@ if [ -d "$FINN_XRT_PATH" ];then
 fi
 
 if [ "$FINN_DOCKER_NO_CACHE" = "1" ]; then
-  export NO_CACHE_STRING="--no-cache"
-else
-  export NO_CACHE_STRING=""
+  FINN_DOCKER_BUILD_EXTRA+="--no-cache"
 fi
 
 # Build the FINN Docker image
 if [ "$FINN_DOCKER_PREBUILT" = "0" ] && [ -z "$FINN_SINGULARITY" ]; then
   # Need to ensure this is done within the finn/ root folder:
   OLD_PWD=$(pwd)
   cd $SCRIPTPATH
-  docker build -f docker/Dockerfile.finn --build-arg XRT_DEB_VERSION=$XRT_DEB_VERSION --build-arg SKIP_XRT=$FINN_SKIP_XRT_DOWNLOAD --build-arg LOCAL_XRT=$LOCAL_XRT --tag=$FINN_DOCKER_TAG $FINN_DOCKER_BUILD_EXTRA $NO_CACHE_STRING .
+  docker build -f docker/Dockerfile.finn --build-arg XRT_DEB_VERSION=$XRT_DEB_VERSION --build-arg SKIP_XRT=$FINN_SKIP_XRT_DOWNLOAD --build-arg LOCAL_XRT=$LOCAL_XRT --tag=$FINN_DOCKER_TAG $FINN_DOCKER_BUILD_EXTRA .
   cd $OLD_PWD
 fi