test: skip test if FreeBSD jail will break it

`test/internet/test-dgram-broadcast-multi-process.js` fails if it is in
a FreeBSD jail. This issue is with the way FreeBSD jails work and not
with Node. Skip the test if in a FreeBSD jail.

PR-URL: https://github.com/nodejs/node/pull/3839
Fixes: https://github.com/nodejs/node/issues/2472


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: Ben Noordhuis <ben@strongloop.com>