Thrift connection pool does not clean up stale connections

Hi,

We are using the thrift client in production and ran into this issue after doing a rolling restart of the cluster. Basically what happens is that when a connection gets disconnected, the corresponding ```Rest.Client``` gets added back into the connection pool without the underlying connection being cleaned up. 

My fix simply closes the underlying connection. The next time the ```Rest.Client``` is used, a new connection will be opened automatically.