add csi-test to vendor

vendor/github.com/golang/mock/sample/imp1/imp1.go

@@ -0,0 +1,17 @@
+package imp1
+
+import "bufio"
+
+type Imp1 struct{}
+
+type ImpT int
+
+type ForeignEmbedded interface {
+	// The return value here also makes sure that
+	// the generated mock picks up the "bufio" import.
+	ForeignEmbeddedMethod() *bufio.Reader
+
+	// This method uses a type in this package,
+	// which should be qualified when this interface is embedded.
+	ImplicitPackage(s string, t ImpT, st []ImpT, pt *ImpT, ct chan ImpT)
+}