Rename Bob's Behavior Failure to CommunicationError

Failure does not express what the error represents. It is only used for communication
errors for quote requests, receiving the XMR transfer proof and sending the encryption signature.

swap/src/protocol/bob/event_loop.rs

@@ -192,7 +192,7 @@ impl EventLoop {
                             debug!("Alice acknowledged encrypted signature");
                         }
                         OutEvent::ResponseSent => {}
-                        OutEvent::Failure(err) => {
+                        OutEvent::CommunicationError(err) => {
                             error!("Communication error: {:#}", err)
                         }
                     }