Implement configurable detach key

Implement configurable detach keys (for `attach`, exec`, `run` and
`start`) using the client-side configuration

- Adds a `--detach-keys` flag to `attach`, `exec`, `run` and `start`
  commands.
- Adds a new configuration field (in `~/.docker/config.json`) to
  configure the default escape keys for docker client.

Signed-off-by: Vincent Demeester <vincent@sbr.pm>

api/client/attach.go

@@ -18,6 +18,7 @@ func (cli *DockerCli) CmdAttach(args ...string) error {
 	cmd := Cli.Subcmd("attach", []string{"CONTAINER"}, Cli.DockerCommands["attach"].Description, true)
 	noStdin := cmd.Bool([]string{"-no-stdin"}, false, "Do not attach STDIN")
 	proxy := cmd.Bool([]string{"-sig-proxy"}, true, "Proxy all received signals to the process")
+	detachKeys := cmd.String([]string{"-detach-keys"}, "", "Override the key sequence for detaching a container")
 
 	cmd.Require(flag.Exact, 1)
 
@@ -46,12 +47,17 @@ func (cli *DockerCli) CmdAttach(args ...string) error {
 		}
 	}
 
+	if *detachKeys != "" {
+		cli.configFile.DetachKeys = *detachKeys
+	}
+
 	options := types.ContainerAttachOptions{
 		ContainerID: cmd.Arg(0),
 		Stream:      true,
 		Stdin:       !*noStdin && c.Config.OpenStdin,
 		Stdout:      true,
 		Stderr:      true,
+		DetachKeys:  cli.configFile.DetachKeys,
 	}
 
 	var in io.ReadCloser