Remove `TODO:method should not throw any exception but currently does`
`mgr.getNode(...)` method is not supposed to throw any type
of exception. It threw two kinds of exceptions: `NotConnectedException`
and `SmackException`.
By using `ThreadedDummyConnection.newInstance()` method,
`NotConnectedException` can be removed. And `SmackException`
can be removed by correctly building the DiscoverInfo packet.
