Load ssh config if possible.

Fix a problem as follows: 

## :smile: :smile: :smile:   Expected: :smile: :smile: :smile: 

    $ tail -5 ~/.ssh/config
    Host example
        HostName buzz.example.com
        User foobar
        Port 2222

    $ sunzi deploy example --sudo
    (((snip snip snip)))  
    $ # DONE!!

This is nice. :+1: 

## :shit: :shit: :shit: Actual: :shit: :shit: :shit:

    $ # It's the same as above...  

    $ sunzi deploy example --sudo
    (((snip snip snip)))  
    ssh: Could not resolve hostname example: Name or service not known

> **ssh: Could not resolve hostname example** :weary:

Can not deploy with ssh config.  :broken_heart: