tiered storage: add s3 endpoint for private s3 implementation

fix https://github.com/chrislusf/seaweedfs/issues/1238

weed/command/scaffold.go

@@ -380,6 +380,7 @@ sequencer_etcd_urls = "http://127.0.0.1:2379"
 	aws_secret_access_key = ""     # if empty, loads from the shared credentials file (~/.aws/credentials).
 	region = "us-east-2"
 	bucket = "your_bucket_name"    # an existing bucket
+	endpoint = ""
 
 # create this number of logical volumes if no more writable volumes
 # count_x means how many copies of data.

weed/storage/backend/s3_backend/s3_backend.go

@@ -36,6 +36,7 @@ type S3BackendStorage struct {
 	aws_secret_access_key string
 	region                string
 	bucket                string
+	endpoint              string
 	conn                  s3iface.S3API
 }
 
@@ -46,7 +47,9 @@ func newS3BackendStorage(configuration backend.StringProperties, configPrefix st
 	s.aws_secret_access_key = configuration.GetString(configPrefix + "aws_secret_access_key")
 	s.region = configuration.GetString(configPrefix + "region")
 	s.bucket = configuration.GetString(configPrefix + "bucket")
-	s.conn, err = createSession(s.aws_access_key_id, s.aws_secret_access_key, s.region)
+	s.endpoint = configuration.GetString(configPrefix + "endpoint")
+
+	s.conn, err = createSession(s.aws_access_key_id, s.aws_secret_access_key, s.region, s.endpoint)
 
 	glog.V(0).Infof("created backend storage s3.%s for region %s bucket %s", s.id, s.region, s.bucket)
 	return
@@ -58,6 +61,7 @@ func (s *S3BackendStorage) ToProperties() map[string]string {
 	m["aws_secret_access_key"] = s.aws_secret_access_key
 	m["region"] = s.region
 	m["bucket"] = s.bucket
+	m["endpoint"] = s.endpoint
 	return m
 }
 

weed/storage/backend/s3_backend/s3_sessions.go

@@ -24,7 +24,7 @@ func getSession(region string) (s3iface.S3API, bool) {
 	return sess, found
 }
 
-func createSession(awsAccessKeyId, awsSecretAccessKey, region string) (s3iface.S3API, error) {
+func createSession(awsAccessKeyId, awsSecretAccessKey, region, endpoint string) (s3iface.S3API, error) {
 
 	sessionsLock.Lock()
 	defer sessionsLock.Unlock()
@@ -34,7 +34,8 @@ func createSession(awsAccessKeyId, awsSecretAccessKey, region string) (s3iface.S
 	}
 
 	config := &aws.Config{
-		Region: aws.String(region),
+		Region:   aws.String(region),
+		Endpoint: aws.String(endpoint),
 	}
 	if awsAccessKeyId != "" && awsSecretAccessKey != "" {
 		config.Credentials = credentials.NewStaticCredentials(awsAccessKeyId, awsSecretAccessKey, "")