Add netbase to docker-stacks-foundation image - fixes #2128 (#2129)

* Add netbase to docker-stacks-foundation image - fixes #2128

* Add a comment describing netbase

Author: AlexHill

images/docker-stacks-foundation/Dockerfile

@@ -30,6 +30,10 @@ RUN apt-get update --yes && \
     bzip2 \
     ca-certificates \
     locales \
+    # - `netbase` provides /etc/{protocols,rpc,services}, part of POSIX
+    #   and required by various C functions like getservbyname and getprotobyname
+    #   https://github.com/jupyter/docker-stacks/pull/2129
+    netbase \
     sudo \
     # - `tini` is installed as a helpful container entrypoint,
     #   that reaps zombie processes and such of the actual executable we want to start