(cloudwatch) high resolution custom metrics (#8958)

* support 1 second resolution Custom Metrics

* upgrade to aws-sdk-go v1.10.18

* simplify period calculation

* add test

* fix period calculation bug

vendor/github.com/aws/aws-sdk-go/private/protocol/xml/xmlutil/build.go

@@ -131,7 +131,6 @@ func (b *xmlBuilder) buildStruct(value reflect.Value, current *XMLNode, tag refl
 			continue
 		}
 
-
 		mTag := field.Tag
 		if mTag.Get("location") != "" { // skip non-body members
 			continue

vendor/github.com/aws/aws-sdk-go/private/protocol/xml/xmlutil/unmarshal.go

@@ -15,7 +15,10 @@ import (
 // needs to match the shape of the XML expected to be decoded.
 // If the shape doesn't match unmarshaling will fail.
 func UnmarshalXML(v interface{}, d *xml.Decoder, wrapper string) error {
-	n, _ := XMLToStruct(d, nil)
+	n, err := XMLToStruct(d, nil)
+	if err != nil {
+		return err
+	}
 	if n.Children != nil {
 		for _, root := range n.Children {
 			for _, c := range root {
@@ -23,7 +26,7 @@ func UnmarshalXML(v interface{}, d *xml.Decoder, wrapper string) error {
 					c = wrappedChild[0] // pull out wrapped element
 				}
 
-				err := parse(reflect.ValueOf(v), c, "")
+				err = parse(reflect.ValueOf(v), c, "")
 				if err != nil {
 					if err == io.EOF {
 						return nil

vendor/github.com/aws/aws-sdk-go/private/protocol/xml/xmlutil/xml_to_struct.go

@@ -40,11 +40,16 @@ func XMLToStruct(d *xml.Decoder, s *xml.StartElement) (*XMLNode, error) {
 	out := &XMLNode{}
 	for {
 		tok, err := d.Token()
-		if tok == nil || err == io.EOF {
-			break
-		}
 		if err != nil {
-			return out, err
+			if err == io.EOF {
+				break
+			} else {
+				return out, err
+			}
+		}
+
+		if tok == nil {
+			break
 		}
 
 		switch typed := tok.(type) {