libtest: Change expected fail state string

Use the value expected by the RTEMS Tester.  There are two separator
characters used ('-' and '_') for the states.  This is a bit
inconsistent.

cpukit/libtest/testbeginend.c

@@ -29,7 +29,7 @@ rtems_printer rtems_test_printer = {
 static const char* const test_state_strings[] =
 {
   "EXPECTED-PASS",
-  "EXPECTED-FAIL",
+  "EXPECTED_FAIL",
   "USER_INPUT",
   "INDETERMINATE",
   "BENCHMARK"