Cherry pick v1.7 into master

vendor/github.com/kolo/xmlrpc/xmlrpc.go

@@ -0,0 +1,19 @@
+package xmlrpc
+
+import (
+	"fmt"
+)
+
+// xmlrpcError represents errors returned on xmlrpc request.
+type xmlrpcError struct {
+	code int
+	err  string
+}
+
+// Error() method implements Error interface
+func (e *xmlrpcError) Error() string {
+	return fmt.Sprintf("error: \"%s\" code: %d", e.err, e.code)
+}
+
+// Base64 represents value in base64 encoding
+type Base64 string