FailureDetectorMBean should expose an integer of machines which are up and down.

Currently FailureDetectorMBean exposes ways to know whether machines are down or not as a string or a map. There is no way to just get a number of down or up machines.
Due to this, the output needs to be parsed to calculate the down machines.
We should add these methods to FailureDetectorMBean
public int getDownEndpointCount();
public int getUpEndpointCount();