Copy modules folder for bessd to load .so files

I0622 03:01:52.720116     1 bessd.cc:456] Loading plugin (attempt 1): /bin/modules/sequential_update.so

RoundRobin       splits packets evenly with round robin
SequentialUpdate updates packet data sequentially in a range
SetMetadata      Set metadata attributes to packets

Signed-off-by: Saikrishna Edupuganti <saikrishna.edupuganti@intel.com>

Dockerfile

@@ -60,8 +60,9 @@ COPY core/ core/
 COPY patches/bess patches
 RUN cp -a ${DPDK_DIR} deps/dpdk-19.11.1 && \
     cat patches/* | patch -p1
-RUN ./build.py bess && \
+RUN ./build.py --plugin sample_plugin bess && \
     cp bin/bessd /bin && \
+    cp -a core/modules /bin && \
     mkdir -p /opt/bess && \
     cp -r bessctl pybess /opt/bess && \
     cp -a core/pb /pb
@@ -90,7 +91,8 @@ RUN apt-get update && \
         https://github.com/secdev/scapy/archive/b65e795c62accd383e1bb6b17cd9f7a9143ae117.zip
 COPY --from=pip /usr/local/lib/python2.7/site-packages/psutil /usr/local/lib/python2.7/site-packages/psutil
 COPY --from=bess-build /opt/bess /opt/bess
-COPY --from=bess-build /bin/bessd /bin
+COPY --from=bess-build /bin/bessd /bin/bessd
+COPY --from=bess-build /bin/modules /bin/modules
 COPY conf /opt/bess/bessctl/conf
 RUN ln -s /opt/bess/bessctl/bessctl /bin
 ENV PYTHONPATH="/opt/bess"