#3019: Add Stunnel as unsupported package

Add Stunnel as an unsupported package to VDT 1.8.1.

Goals:

1) Add Stunnel. http://www.stunnel.org/ Call the package Unsup-Stunnel.

2) Probably link against system SSL, not Globus SSL. Feel free to argue
if you don't agree.

3) Understand configuration and setup well. Some specific questions:

3a) Our eventual goal is to use this with syslog-ng, so ask questions
about the configuration that help us understand that, even though
hooking it up to syslog-ng isn't part of this ticket.

3b) Do we have to distribute certificates, or can we distribute
certificate DNs and rely on the fact that we trust the CAs?

3c) Should we use the host certificate (and therefore run as root?) or a
service certificate?

4) I think we should do this on a branch, since it might take a while
before it's ready to release.

Notes:

* Brian Tierney made some instructions for setting up stunnel for
syslong-ng for the OSG VTB. I don't know how much they will help with
this task, but we can refer to them:

https://twiki.grid.iu.edu/twiki/bin/view/Integration/VTBSyslogNGstunnel

* I built stunnel once, and the build was very straightforward except
for an interactive step. This interactive step is the only bit that
might make a Metronome build tricky, and it shouldn't be all that tricky.