Sync peers FQDN (#584)

Use stdout and stderr log path only if on Linux and attempt to create the path

Update status system with FQDN fields and 
status command to display the domain names of remote and local peers

Set some DNS logs to tracing

update readme file

client/status/status.go

@@ -10,6 +10,7 @@ import (
 type PeerState struct {
 	IP                     string
 	PubKey                 string
+	FQDN                   string
 	ConnStatus             string
 	ConnStatusUpdate       time.Time
 	Relayed                bool
@@ -23,6 +24,7 @@ type LocalPeerState struct {
 	IP              string
 	PubKey          string
 	KernelInterface bool
+	FQDN            string
 }
 
 // SignalState contains the latest state of a signal connection
@@ -136,6 +138,22 @@ func (d *Status) UpdatePeerState(receivedState PeerState) error {
 	return nil
 }
 
+// UpdatePeerFQDN update peer's state fqdn only
+func (d *Status) UpdatePeerFQDN(peerPubKey, fqdn string) error {
+	d.mux.Lock()
+	defer d.mux.Unlock()
+
+	peerState, ok := d.peers[peerPubKey]
+	if !ok {
+		return errors.New("peer doesn't exist")
+	}
+
+	peerState.FQDN = fqdn
+	d.peers[peerPubKey] = peerState
+
+	return nil
+}
+
 // GetPeerStateChangeNotifier returns a change notifier channel for a peer
 func (d *Status) GetPeerStateChangeNotifier(peer string) <-chan struct{} {
 	d.mux.Lock()