lib: add more self-tests around the igt_exit checks.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

tests/Makefile.am

@@ -159,6 +159,8 @@ kernel_tests = \
 	$(NULL)
 
 TESTS_testsuite = \
+	igt_no_exit \
+	igt_no_exit_list_only \
 	igt_fork_helper \
 	igt_list_only \
 	$(NULL)
@@ -167,6 +169,11 @@ TESTS = \
 	$(TESTS_testsuite) \
 	$(NULL)
 
+XFAIL_TESTS = \
+	igt_no_exit \
+	igt_no_exit_list_only \
+	$(NULL)
+
 list-single-tests:
 	@echo TESTLIST
 	@echo ${single_kernel_tests}