rpc unit tests can fail due to race condition

rpc unit tests can fail due to race condition

The rpc unit tests can fail in fullrun.exp due to a failure to drain
output from the server in expire.exp.  This commit works around the
problem by calling flush_server, but a real synchronization method
should probably be implemented, perhaps by having the server log when
a client disconnects.

	* rpc_test.0/expire.exp (overlap): Add another call to
	flush_server to make a race condition a little less likely.  There
	really should be better synchronization, as this test suite is
	just full of race conditions waiting to happen.

ticket: new
status: open

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@14979 dc483132-0cff-0310-8789-dd5450dbe970