Add Type() method on flags for compat with pflag library

Allows our flag objects to be used with both golang flags and pflags

pkg/util/list.go

@@ -33,3 +33,7 @@ func (sl *StringList) Set(value string) error {
 	}
 	return nil
 }
+
+func (*StringList) Type() string {
+	return "stringList"
+}

pkg/util/net.go

@@ -37,6 +37,10 @@ func (ip *IP) Set(value string) error {
 	return nil
 }
 
+func (*IP) Type() string {
+	return "ip"
+}
+
 // IPNet adapts net.IPNet for use as a flag.
 type IPNet net.IPNet
 
@@ -53,3 +57,7 @@ func (ipnet *IPNet) Set(value string) error {
 	*ipnet = IPNet(*n)
 	return nil
 }
+
+func (*IPNet) Type() string {
+	return "ipNet"
+}