test-appliance: fix use of undefined variable in gen_results_summary

This fixes the following Python error when no tests were run:

Traceback (most recent call last):
File "/usr/local/bin/gen_results_summary", line 22, in <module>
main()
File "/usr/local/bin/gen_results_summary", line 19, in main
sys.exit('No results file found in ' + results_dir)
NameError: global name 'results_dir' is not defined

---
 .../test-appliance/files/usr/local/bin/gen_results_summary      | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index be4401e..57c4a08 100755
@@ -16,7 +16,7 @@ def main():
 
     if gen_results_summary(args.results_dir, args.output_file,
                            args.merge_file, args.verbose) == 0:
-        sys.exit('No results file found in ' + results_dir)
+        sys.exit('No results file found in ' + args.results_dir)
 
 if __name__ == "__main__":
     main()

2.17.0.rc1.321.gba9d0f2565-goog

Thanks, applied.

- Ted