Secured and customizable PLPython and PLR on Postgresql

Hi all,

As you know PLPython and PLR are untrusted language, which means only DBA
could create these UDFs(very inconvenient). Moreover it's also hard to
supply user specific Python/R env for different data scientists.

We are working on an open source project to make PLPython and PLR trusted
and customizable. The project is called PLContainer, which use Docker
Container as the sandbox to avoid malicious user breaking Postgresql
database or even the whole host machine.

Now there is a basic version which could support PLContainer on PG9.6
(Thanks krait007 and markwort for the contribution). We still have a lot of
issues to make it production ready and share with more peoples. [Github
umbrella project](https://github.com/greenplum-db/plcontainer/projects/1)

If you are interested in it, feel free to try it. Your suggestion and
contribution will be appreciated.
--
Thanks

Hubert Zhang