Make a process test faster.

Make a process test faster.

The test 'process-tests/fd-setsize-no-crash/make-process' used to call
'sleep' to ensure that enough processes are live to trigger a
FD_SETSIZE overflow.  However, we can just call 'cat' instead and
close standard input when done.  That way, we only wait as long as
needed.

* process-tests.el
(process-tests/fd-setsize-no-crash/make-process): Invoke 'cat' instead
of 'sleep'.  Close standard input to exit the 'cat' processes.