Run RPC tests with one invocation of DejaGnu rather than two

Run RPC tests with one invocation of DejaGnu rather than two

* Makefile.in (unit-test-body): Combine -tcp and -udp versions, setting PASS
instead of PROT.
* configure.in: Set and substitute PASS instead of UDP_TEST.
* config/unix.exp: Don't invoke rpc_test_start.  Set MULTIPASS, including a
setting for PROT and a dummy to trigger rpc_test_start invocation.
(rpc_test_start): If a server has already been started, call rpc_test_exit to
verify that it's still running.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@12503 dc483132-0cff-0310-8789-dd5450dbe970