Add the docker images for CoAP test servers

This change includes:
- Docker image for the test server to test non-secure and PSK-based
  CoAP security modes.
- Docker image for the test server to test X.509 certificate-based
  CoAP security mode.

Change-Id: Ice661917591ecaee8ebc3500209bcffc08981f65
Reviewed-by: Ryan Chu <ryan.chu@qt.io>

coin/provisioning/common/shared/testserver/californium/Dockerfile

@@ -0,0 +1,15 @@
+FROM ubuntu:18.04
+
+RUN apt-get update && apt-get -y install git maven default-jdk avahi-daemon
+
+RUN mkdir -p /root/src/
+
+# Get californium-based CoAP test server
+WORKDIR /root/src
+RUN git clone https://github.com/selart/californium.git
+WORKDIR /root/src/californium
+RUN mvn clean install -q -DskipTests
+
+WORKDIR /
+
+EXPOSE 5683/udp 5684/udp