Update github.com/stretchr/testify to v1.2.1

cd $GOPATH/src/k8s.io/kubernetes
hack/godep-restore.sh
rm -rf Godeps
rm -rf vendor
hack/godep-save.sh
hack/update-staging-godeps.sh

vendor/github.com/stretchr/testify/require/requirements.go

@@ -6,4 +6,24 @@ type TestingT interface {
 	FailNow()
 }
 
+type tHelper interface {
+	Helper()
+}
+
+// ComparisonAssertionFunc is a common function prototype when comparing two values.  Can be useful
+// for table driven tests.
+type ComparisonAssertionFunc func(TestingT, interface{}, interface{}, ...interface{})
+
+// ValueAssertionFunc is a common function prototype when validating a single value.  Can be useful
+// for table driven tests.
+type ValueAssertionFunc func(TestingT, interface{}, ...interface{})
+
+// BoolAssertionFunc is a common function prototype when validating a bool value.  Can be useful
+// for table driven tests.
+type BoolAssertionFunc func(TestingT, bool, ...interface{})
+
+// ValuesAssertionFunc is a common function prototype when validating an error value.  Can be useful
+// for table driven tests.
+type ErrorAssertionFunc func(TestingT, error, ...interface{})
+
 //go:generate go run ../_codegen/main.go -output-package=require -template=require.go.tmpl -include-format-funcs