tests/gem_exec_nop: implemented correct SKIP reporting

I think I need a testsuite for test writing.
diff --git a/tests/gem_exec_nop.c b/tests/gem_exec_nop.c
index 70dfe96..8608592 100644
--- a/tests/gem_exec_nop.c
+++ b/tests/gem_exec_nop.c
@@ -43,6 +43,8 @@
 #include "drmtest.h"
 #include "intel_gpu_tools.h"
 
+bool skipped_all = true;
+
 static double elapsed(const struct timeval *start,
 		      const struct timeval *end,
 		      int loop)
@@ -91,6 +93,8 @@
 {
 	int count;
 
+	skipped_all = false;
+
 	for (count = 1; count <= 1<<17; count <<= 1) {
 		struct timeval start, end;
 
@@ -135,5 +139,5 @@
 
 	close(fd);
 
-	return 0;
+	return skipped_all ? 77 : 0;
 }