Assume local endpoints appropriately in k8s deployments (#8375)

On Kubernetes/Docker setups DNS resolves inappropriately
sometimes where there are situations same endpoints with
multiple disks come online indicating either one of them
is local and some of them are not local. This situation
can never happen and its only a possibility in orchestrated
deployments with dynamic DNS. Following code ensures that we
treat if one of the endpoint says its local for a given host
it is true for all endpoints for the same host. Following code
ensures that this assumption is true and it works in all
scenarios and it is safe to assume for a given host.

This PR also adds validation such that we do not crash the
server if there are bugs in the endpoints list in dsync
initialization.

Thanks to Daniel Valdivia <hola@danielvaldivia.com> for
reproducing this, this fix is needed as part of the
https://github.com/minio/m3 project.

cmd/namespace-lock.go

@@ -53,8 +53,9 @@ type RWLocker interface {
 
 // Initialize distributed locking only in case of distributed setup.
 // Returns lock clients and the node index for the current server.
-func newDsyncNodes(endpoints EndpointList) (clnts []dsync.NetLocker, myNode int) {
+func newDsyncNodes(endpoints EndpointList) (clnts []dsync.NetLocker, myNode int, err error) {
 	myNode = -1
+
 	seenHosts := set.NewStringSet()
 	for _, endpoint := range endpoints {
 		if seenHosts.Contains(endpoint.Host) {
@@ -66,26 +67,27 @@ func newDsyncNodes(endpoints EndpointList) (clnts []dsync.NetLocker, myNode int)
 		if endpoint.IsLocal {
 			myNode = len(clnts)
 
-			receiver := &lockRESTServer{
+			globalLockServer = &lockRESTServer{
 				ll: &localLocker{
 					serverAddr:      endpoint.Host,
 					serviceEndpoint: lockServicePath,
 					lockMap:         make(map[string][]lockRequesterInfo),
 				},
 			}
-
-			globalLockServer = receiver
-			locker = receiver.ll
+			locker = globalLockServer.ll
 		} else {
-			host, err := xnet.ParseHost(endpoint.Host)
-			logger.FatalIf(err, "Unable to parse Lock RPC Host")
+			var host *xnet.Host
+			host, err = xnet.ParseHost(endpoint.Host)
 			locker = newlockRESTClient(host)
 		}
 
 		clnts = append(clnts, locker)
 	}
 
-	return clnts, myNode
+	if myNode == -1 {
+		return clnts, myNode, errors.New("no endpoint pointing to the local machine is found")
+	}
+	return clnts, myNode, err
 }
 
 // newNSLock - return a new name space lock map.