Switch to ginkgo/gomega for tests

This switches over to ginkgo/gomega for tests, which makes writing
certain tests easier/more fluent in the future.

vendor/github.com/onsi/gomega/matchers/attributes_slice.go

@@ -0,0 +1,14 @@
+package matchers
+
+import (
+	"encoding/xml"
+	"strings"
+)
+
+type attributesSlice []xml.Attr
+
+func (attrs attributesSlice) Len() int { return len(attrs) }
+func (attrs attributesSlice) Less(i, j int) bool {
+	return strings.Compare(attrs[i].Name.Local, attrs[j].Name.Local) == -1
+}
+func (attrs attributesSlice) Swap(i, j int) { attrs[i], attrs[j] = attrs[j], attrs[i] }