Specify multiple interfaces to look for an address on.

This allows us to start Cortex on the Mac.

Signed-off-by: Tom Wilkie <tom.wilkie@gmail.com>

pkg/util/flagext/strings.go

@@ -0,0 +1,18 @@
+package flagext
+
+import (
+	"fmt"
+)
+
+type Strings []string
+
+// String implements flag.Value
+func (ss Strings) String() string {
+	return fmt.Sprintf("%s", []string(ss))
+}
+
+// Set implements flag.Value
+func (ss *Strings) Set(s string) error {
+	*ss = append(*ss, s)
+	return nil
+}