Update example symbolic link creation in Dockerfile.template

[yaooqinn]

What changes were proposed in this pull request?

Update example symbolic link creation in Dockerfile.template

Why are the changes needed?

requirement from the docker official community

Does this PR introduce any user-facing change?

no

How was this patch tested?

locally ran tools/template.py

    tar -xf spark.tgz --strip-components=1; \
    chown -R spark:spark .; \
    mv jars /opt/spark/; \
    mv RELEASE /opt/spark/; \
    mv bin /opt/spark/; \
    mv sbin /opt/spark/; \
    mv kubernetes/dockerfiles/spark/decom.sh /opt/; \
    mv examples /opt/spark/; \
    ln -s "$(basename /opt/spark/examples/jars/spark-examples_*.jar)" /opt/spark/examples/jars/spark-examples.jar; \
    mv kubernetes/tests /opt/spark/; \
    mv data /opt/spark/; \
    mv python/pyspark /opt/spark/python/pyspark/; \
    mv python/lib /opt/spark/python/lib/; \
    mv R /opt/spark/; \
    chmod a+x /opt/decom.sh; \
    cd ..; \
    rm -rf "$SPARK_TMP";

[yaooqinn]

cc @dongjoon-hyun

[dongjoon-hyun]

+1, LGTM. Thank you, @yaooqinn !