This implements a default path of /tftpboot/%s if no path is provided,
and adds host name substitution for %s, with a fall back to the IP address,
as provided by the kernel's nfsroot handling.
The test suite is updated to test this functionality.
The full tests take over 6 minutes to run, and commenting out unneeded
ones is time consuming -- this change lets me comment out one line to
temporarily avoid an entire class of tests.
Test additional combinations of command line and DHCP option formats. This
is by no means the complete list, but gets us started with some common ones.
When debugging, this is still needed as we won't be redirecting out
output to /dev/null or a file. However, we need to guard against not
having a terminal.
David Dillow