[krbdev.mit.edu #1233] need to disable /dev/random use for testing

[Ken Raeburn via RT]

On relatively idle machines, nightly tests run via cron are failing
because kadmin takes too long to initialize at startup, because it
blocks reading from /dev/random.  For testing purposes, we don't care
how good the random numbers are, as long as they're at least "sort of"
good; using /dev/urandom is more than adequate.

A new config file (krb5.conf probably) option to explicitly turn off
the use of /dev/random should be created.  Probably using "insecure"
and "entropy" in the name, something like that.  Whether the
application-level code or the crypto library code should act on it is
to be decided.