Add --shell argument

Add subshell argument --shell. Currently, support only bash, which is
also the default value.

cli/commands.go

@@ -355,5 +355,9 @@ func GetKubeConfig(c *cli.Context) error {
 }
 
 func Shell(c *cli.Context) error {
+	if c.String("shell") != "bash" {
+		return fmt.Errorf("%s is not supported. Only bash is supported", c.String("shell"))
+	}
+
 	return bashShell(c.String("name"), c.String("command"))
 }

main.go

@@ -59,6 +59,11 @@ func main() {
 					Name:  "command, c",
 					Usage: "Run a shell command in the context of the cluster",
 				},
+				cli.StringFlag{
+					Name:  "shell, s",
+					Value: "bash",
+					Usage: "Sub shell type. Only bash is supported. (default bash)",
+				},
 			},
 			Action: run.Shell,
 		},