Checks whether this connection has gone down.
Network connections may get closed during some time of inactivity
for several reasons. The next time a read is attempted on such a
connection it will throw an IOException.
This method tries to alleviate this inconvenience by trying to
find out if a connection is still usable. Implementations may do
that by attempting a read with a very small timeout. Thus this
method may block for a small amount of time before returning a result.
It is therefore an expensive operation.
true if attempts to use this connection are
likely to succeed, or false if they are likely
to fail and this connection should be closed