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/freecoap/Dockerfile

@@ -0,0 +1,20 @@
+FROM ubuntu:18.04
+
+RUN apt-get update && apt-get -y install git avahi-daemon autoconf automake libtool make libgnutls28-dev
+
+RUN mkdir -p /root/src/
+
+# Get FreeCoAP test server
+WORKDIR /root/src
+RUN git clone https://github.com/keith-cullen/FreeCoAP.git
+WORKDIR /root/src/FreeCoAP
+RUN autoreconf --install
+RUN ./configure
+RUN make
+RUN make install
+WORKDIR /root/src/FreeCoAP/sample/time_server
+RUN make
+
+WORKDIR /
+
+EXPOSE 5685/udp