TUN-8737: update metrics server port selection

## Summary
Update how metrics server binds to a listener by using a known set of ports whenever the default address is used with the fallback to a random port in case all address are already in use. The default address changes at compile time in order to bind to a different default address when the final deliverable is a docker image.

Refactor ReadyServer tests.

Closes TUN-8737

tunnelstate/conntracker.go

@@ -9,7 +9,7 @@ import (
 )
 
 type ConnTracker struct {
-	sync.RWMutex
+	mutex sync.RWMutex
 	// int is the connection Index
 	connectionInfo map[uint8]ConnectionInfo
 	log            *zerolog.Logger
@@ -20,43 +20,39 @@ type ConnectionInfo struct {
 	Protocol    connection.Protocol
 }
 
-func NewConnTracker(log *zerolog.Logger) *ConnTracker {
+func NewConnTracker(
+	log *zerolog.Logger,
+) *ConnTracker {
 	return &ConnTracker{
 		connectionInfo: make(map[uint8]ConnectionInfo, 0),
 		log:            log,
 	}
 }
 
-func MockedConnTracker(mocked map[uint8]ConnectionInfo) *ConnTracker {
-	return &ConnTracker{
-		connectionInfo: mocked,
-	}
-}
-
 func (ct *ConnTracker) OnTunnelEvent(c connection.Event) {
 	switch c.EventType {
 	case connection.Connected:
-		ct.Lock()
+		ct.mutex.Lock()
 		ci := ConnectionInfo{
 			IsConnected: true,
 			Protocol:    c.Protocol,
 		}
 		ct.connectionInfo[c.Index] = ci
-		ct.Unlock()
+		ct.mutex.Unlock()
 	case connection.Disconnected, connection.Reconnecting, connection.RegisteringTunnel, connection.Unregistering:
-		ct.Lock()
+		ct.mutex.Lock()
 		ci := ct.connectionInfo[c.Index]
 		ci.IsConnected = false
 		ct.connectionInfo[c.Index] = ci
-		ct.Unlock()
+		ct.mutex.Unlock()
 	default:
 		ct.log.Error().Msgf("Unknown connection event case %v", c)
 	}
 }
 
 func (ct *ConnTracker) CountActiveConns() uint {
-	ct.RLock()
-	defer ct.RUnlock()
+	ct.mutex.RLock()
+	defer ct.mutex.RUnlock()
 	active := uint(0)
 	for _, ci := range ct.connectionInfo {
 		if ci.IsConnected {
@@ -69,8 +65,8 @@ func (ct *ConnTracker) CountActiveConns() uint {
 // HasConnectedWith checks if we've ever had a successful connection to the edge
 // with said protocol.
 func (ct *ConnTracker) HasConnectedWith(protocol connection.Protocol) bool {
-	ct.RLock()
-	defer ct.RUnlock()
+	ct.mutex.RLock()
+	defer ct.mutex.RUnlock()
 	for _, ci := range ct.connectionInfo {
 		if ci.Protocol == protocol {
 			return true