Change failure to talk to DNS seeders to debug.

This is just a temporary failure and shouldn't be a warning.  Also,
remove redundant prefix on profile server log print while here.

btcd.go

@@ -44,7 +44,7 @@ func btcdMain() error {
 	if cfg.Profile != "" {
 		go func() {
 			listenAddr := net.JoinHostPort("", cfg.Profile)
-			log.Infof("BTCD: Profile server listening on %s", listenAddr)
+			log.Infof("Profile server listening on %s", listenAddr)
 			log.Errorf("%v", http.ListenAndServe(listenAddr, nil))
 		}()
 	}

discovery.go

@@ -158,7 +158,7 @@ func dnsDiscover(seeder string, proxy string) []net.IP {
 			seederPlusProxy = fmt.Sprintf("%s (proxy %s)",
 				seeder, proxy)
 		}
-		log.Warnf("DISC: Failed to fetch dns seeds "+
+		log.Debugf("DISC: Unable to fetch dns seeds "+
 			"from %s: %v", seederPlusProxy, err)
 		return []net.IP{}
 	}