Added feature connect to ssh on alternate ports

[ithouse]

Hello Adam,
I had to access some servers where sshd is configured to listen to other ports than 22
With this commit you can do
remote = Rush::Box.new("example.com:2222")
2 tests added, no tests broken

[mattbailey]

+1 on this pull request, would really like this feature.

[empjustine]

Sorry for ressurecting 2 years old issue but, isn't editing ~/.ssh/config better?

Host example
    HostName example.com
    Port 2222

[s-mage]

@empjustine sure it is (I'm sorry too).