Multiple user support

we need support for multiple user, and add one default user

example:
```
- hostname: "hostname"
 user: "user"
 password: "MTIzCgXD"
 port: "22"
 key: |
   MTIzNDU2Nzg5MTAK
default_user: true
```

so we can connect with
```
hermes connect user@hostname
```

or

```
hermes connect hostname # default user
```