lib: add an exit code to use when invalid options are specified

Signed-off-by: Thomas Wood <thomas.wood@intel.com>

lib/igt_core.h

@@ -59,6 +59,13 @@
  */
 #define IGT_EXIT_SUCCESS 0
 
+/**
+ * IGT_EXIT_INVALID
+ *
+ * Exit status indicating an invalid option or subtest was specified
+ */
+#define IGT_EXIT_INVALID 79
+
 
 bool __igt_fixture(void);
 void __igt_fixture_complete(void);