lntest: add SendCoinsUnconfimed method
lntest: add SendCoinsUnconfimed method

In this commit, we add a new method to the network harness that allows
us to send funds to another party without confirming the transaction.
This will be useful for testing funding channels with outputs that have
not been confirmed yet.

aakselrod/lnd,LightningNetwork/lnd,LightningNetwork/lnd,aakselrod/lnd