stunnel: Add a stunnel-wrapper image

stunnel: Add a stunnel-wrapper image

Make it easy to wrap arbitrary ports with stunnel.

The explicit pid configuration avoids errors like:

  ... stunnel: ... Cannot create pid file /var/lib/run/stunnel/stunnel.pid
  ... stunnel: ... create: No such file or directory (2)

which is probably just a wart in Gentoo's stunnel packaging.