prefork tests: disable restart tests MIT

prefork tests: disable restart tests MIT

The prefork restart tests use the kdc to test restart back off.  These
tests need to use a process that has not been restarted to ensure that
the process restart counters are sitting at 0 when the tests start.

As MIT kerberos is experimental the heimdal builds will still ensure
that this functionality is tested.

At some stage the echo server should be converted to run in pre-fork and
this process can then be used to test the restart backoff.

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>