Move ListOps to utils submodule

This will be needed for later use in docker-init without a docker
dependency

utils/utils.go

@@ -21,6 +21,18 @@ import (
 	"time"
 )
 
+// ListOpts type
+type ListOpts []string
+
+func (opts *ListOpts) String() string {
+	return fmt.Sprint(*opts)
+}
+
+func (opts *ListOpts) Set(value string) error {
+	*opts = append(*opts, value)
+	return nil
+}
+
 // Go is a basic promise implementation: it wraps calls a function in a goroutine,
 // and returns a channel which will later return the function's return value.
 func Go(f func() error) chan error {