test.py: fail if given test name not found

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Message-Id: <20190411092041.24712-1-bhalevy@scylladb.com>

test.py

@@ -246,6 +246,9 @@ if __name__ == "__main__":
 
     if args.name:
         test_to_run = [t for t in test_to_run if args.name in t[0]]
+        if not test_to_run:
+            print("Test {} not found".format(args.name))
+            sys.exit(1)
 
     failed_tests = []