Reduce risk for false negatives

Monitor connectivity and response test may fail due to server being extremely busy. MaxScale should consider the server alive if routers are receiving data from server. Perhaps a special status flag is needed, e.g. "really busy" or "saturated"?

Currently, the above scenario should not be too threatening, since when a monitor labels a server as [Down], it actually commands all routing connections to that server to hangup. Once this happens, and the server detects that the clients have disconnected, the server would likely close any attached sessions and free resources. This would then lead to the server being available for MaxScale monitor connections once more. At least, this is what would happen with one MaxScale. With multiple MaxScales, a server could be saturated by MXS1 and not connectable by monitor from MXS2.