Adding `--open` option in `start/restart`, fixing #172

Open a url in the preferred application

Usage:

```sh
$ azk start -o [system]
```

help description:

```sh
$ azk help start

Usage: $ azk [options] start [options] [system]

Starts an instance of the system(s)

options:

  --verbose, -v, -vv  Sets the level of detail (default: false) - multiples supported
  --reprovision, -R   Force the provisioning actions before starting an instance (default: false)
  --open="", -o       Open a url of system in the preferred application
```
Updating `--open` option

Now the `--open` option in command start and restart open the default system.
Adding support to vbox in mounts folders.
Merge branch 'feature/cmd_open' into develop

Conflicts:
	CHANGELOG.md
	src/cmds/start.js
Fixing start agent