Add alpn-boot support for HTTP2 plugin

Dockerfile

@@ -4,6 +4,7 @@ STOPSIGNAL SIGKILL
 ENV JMETER_VERSION 5.1.1
 ENV JMETER_HOME /opt/apache-jmeter-${JMETER_VERSION}
 ENV JMETER_BIN ${JMETER_HOME}/bin
+ENV ALPN_VERSION 8.1.13.v20181017
 ENV PATH ${JMETER_BIN}:$PATH
 COPY entrypoint.sh /usr/local/bin/
 RUN chmod +x /usr/local/bin/entrypoint.sh \
@@ -25,7 +26,12 @@ RUN chmod +x /usr/local/bin/entrypoint.sh \
  && sed -i '/PrintGCDetails/s/^# /: "${/g' ${JMETER_BIN}/jmeter && sed -i '/PrintGCDetails/s/$/}"/g' ${JMETER_BIN}/jmeter \
  && chmod +x ${JMETER_HOME}/bin/*.sh \
  && jmeter --version \
+ && curl --location --silent --show-error --output /opt/alpn-boot-${ALPN_VERSION}.jar http://central.maven.org/maven2/org/mortbay/jetty/alpn/alpn-boot/${ALPN_VERSION}/alpn-boot-${ALPN_VERSION}.jar \
  && rm -fr /tmp/*
+
+# Required for HTTP2 plugins
+ENV JVM_ARGS -Xbootclasspath/p:/opt/alpn-boot-${ALPN_VERSION}.jar
+
 WORKDIR /jmeter
 ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]
 CMD ["jmeter", "--?"]