Tools: fixed wait_for_alt

should be a min alt. This is needed for Flip test to pass with new
model, as it doesn't lose as much height as the old model. So it
starts above the min alt

Tools/autotest/arducopter.py

@@ -137,9 +137,9 @@ class AutoTestCopter(AutoTest):
         self.progress("TAKEOFF COMPLETE")
 
     def wait_for_alt(self, alt_min=30, timeout=30):
-        """Wait for altitude to be reached."""
+        """Wait for minimum altitude to be reached."""
         self.wait_altitude(alt_min - 1,
-                           (alt_min + 5),
+                           (alt_min + 500),
                            relative=True,
                            timeout=timeout)