Add a test of the random director that uses actual randomness.

This will be skipped on platforms where srandom(1) does not result
in the same deterministic sequence of random numbers as on FreeBSD
and Linux.



git-svn-id: http://www.varnish-cache.org/svn/branches/2.0@3535 d4fa192b-c00b-0410-8231-f00ffab90ce4