examples: fix the image name prefix

Signed-off-by: llhuii <liulinghui@huawei.com>

examples/build_image.sh

@@ -100,5 +100,5 @@ dockerfiles=($(echo "${dockerfiles[@]}" | tr ' ' '\n' | sort -u))
 for dockerfile in ${dockerfiles[@]}; do
    echo "Building $dockerfile" 
    example_name=${dockerfile/.Dockerfile}
-   docker build -f $dockerfile -t ${IMAGE_REPO}/${example_name}:${IMAGE_TAG} --label sedna=examples ..
-done
+   docker build -f $dockerfile -t ${EXAMPLE_REPO_PREFIX}${example_name}:${IMAGE_TAG} --label sedna=examples ..
+done