RTEMS Tester TFTP Timeout Fixes

[chrisj at rtems.org]

Hi,

This is v2 of the fixes for timouts for TFTP testing. I am testing
i386/pc686 on hardware using grub to PXE boot the executable. This
configuration is different to uboot because a failure to load the
executable stops loading and this hangs the tester. A uboot target
keeps attempting TFTP loads and that recovers while grub does not.
The fixes here add two new user variables:

 session_timeout = 20
 target_reset_on_timeout = yes

The session_timeout is a new timeout for the TFTP session to
timeout if a client does not happen. The second will cause
a reset on a timeout. The timeouts are a console timeout or a test
too long timeout.

Chris