use t_inetd with a ready message and avoid waiting a lot in non-root tests

use t_inetd with a ready message and avoid waiting a lot in non-root tests

Change t_inetd to print a ready message when it has started listening
on the indicated port number.

Look for this message in sample.exp rather than waiting an arbitrary
(and usually excessive) 2s each time for the inetd-mode tests.  Use
run_once to perform the standalone-mode test only once per test suite
invocation.

Change rsh and rcp tests to start the servers via t_inetd and avoid
excessive waiting at startup.

In some of my tests, this reduces the tests/dejagnu tests from taking
over 6 minutes to taking around 2 minutes.

(This does mean the server process will no longer have started up
before we launch the client, so it may be slower to respond, but it'll
still be faster than the 2s delay we used before even trying to
connect.)

We can probably eliminate the -D option code from krshd.c now.

The tests run as root (rlogin, telnet) still need updating.

ticket: 6355
target_version: 1.7
tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@21855 dc483132-0cff-0310-8789-dd5450dbe970