qa: mininode: Clearer error message on invalid magic bytes

Author: MarcoFalke

test/functional/test_framework/mininode.py

@@ -171,7 +171,7 @@ def _on_data(self):
                 if len(self.recvbuf) < 4:
                     return
                 if self.recvbuf[:4] != self.magic_bytes:
-                    raise ValueError("got garbage %s" % repr(self.recvbuf))
+                    raise ValueError("magic bytes mismatch: {} != {}".format(repr(self.magic_bytes), repr(self.recvbuf)))
                 if len(self.recvbuf) < 4 + 12 + 4 + 4:
                     return
                 command = self.recvbuf[4:4+12].split(b"\x00", 1)[0]