fundingManager: conditional select on arbiterChan and peer.newChannels
fundingManager: conditional select on arbiterChan and peer.newChannels

This commit adds a select statement for sending on the fundingManager's
arbiterChan and the peer's newChannels channel. This makes sure we won't
be blocked sending on these channels in case of a shutdown.

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