Add Debian Jessie build image

This image is meant to be used to build packages for the Jessie release of Debian. See debian/nginx-build.

debian/jessie/Dockerfile

 FROM debian:jessie
-ADD  setup.sh /opt/
-RUN  /bin/bash /opt/setup.sh
+COPY setup.sh /opt/
+RUN /bin/bash /opt/setup.sh