Update vendored azure-sdk-for-go

Updating to a recent version of Azure Storage SDK to be
able to patch some memory leaks through configurable HTTP client
changes which were made possible by recent patches to it.

Signed-off-by: Ahmet Alp Balkan <ahmetalpbalkan@gmail.com>

vendor/github.com/Azure/azure-sdk-for-go/storage/util.go

@@ -11,6 +11,7 @@ import (
 	"io/ioutil"
 	"net/http"
 	"net/url"
+	"reflect"
 	"time"
 )
 
@@ -69,3 +70,16 @@ func xmlMarshal(v interface{}) (io.Reader, int, error) {
 	}
 	return bytes.NewReader(b), len(b), nil
 }
+
+func headersFromStruct(v interface{}) map[string]string {
+	headers := make(map[string]string)
+	value := reflect.ValueOf(v)
+	for i := 0; i < value.NumField(); i++ {
+		key := value.Type().Field(i).Tag.Get("header")
+		val := value.Field(i).String()
+		if val != "" {
+			headers[key] = val
+		}
+	}
+	return headers
+}