Add printing of creating date

Change-Id: Ida3aeb09365c3c368bfd6d48ef458403add1ead1
diff --git a/Dockerfile b/Dockerfile
index 4c8fcab..c6e60e9 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -97,6 +97,9 @@
 RUN apt-get -y autoremove; apt-get -y clean;
 RUN rm -rf /root/.cache
 RUN rm -rf /var/lib/apt/lists/*
+
+RUN echo "BUILD_TIMESTAMP=$(date '+%Y-%m-%d-%H-%M-%S' -u)" > /etc/build_timestamp
+
 #
 COPY bin/entrypoint.sh /usr/bin/entrypoint.sh
 COPY bin/run_tempest.sh /usr/bin/run-tempest