Fix warning in docker CLI when swarm ca --ca-cert, etc. flags are passed,

and add a test.

Signed-off-by: Ying Li <ying.li@docker.com>
(cherry picked from commit 4615c92f66)

Conflicts:
components/cli/cli/command/swarm/ca_test.go
Signed-off-by: Andrew Hsu <andrewhsu@docker.com>

components/cli/cli/command/swarm/ca.go

@@ -61,7 +61,7 @@ func runRotateCA(dockerCli command.Cli, flags *pflag.FlagSet, opts caOptions) er
 	}
 
 	if !opts.rotate {
-		for _, f := range []string{flagCACert, flagCAKey, flagCACert, flagExternalCA} {
+		for _, f := range []string{flagCACert, flagCAKey, flagCertExpiry, flagExternalCA} {
 			if flags.Changed(f) {
 				return fmt.Errorf("`--%s` flag requires the `--rotate` flag to update the CA", f)
 			}