tests: Make setup errors in grub-fs-tester hard errors

tests: Make setup errors in grub-fs-tester hard errors

When a test program fails because it failed to setup the test properly, this
does not indicate a failure in what is attempting to be tested because the
test is never run. So exit with a hard error exit status to note this
difference. This will allow easier detection of tests that are not actually
being run and those that are really failing.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>