Fixes SSH gateway remote SSH port option handling

Description

I recently discovered that knife-cloud was incorrectly handling options for specifying the remote SSH port of the node you want to bootstrap when using an SSH gateway. The problem was that it was only honoring the deprecated --ssh-port option and not the replacement option --connection-port. It also lacked a default of port 22, so when --ssh-port was unspecified, nil was being passed as the remote port for the SSH gateway. From my cursory reading of RFC 4254 not passing a remote port is unspecified behavior so I've added a default for the remote port.

Types of changes

[x] Bug fix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)
[x] Chore (non-breaking change that does not add functionality or fix an issue)

Checklist:

[x] I have read the CONTRIBUTING document.
[x] I have run the pre-merge tests locally and they pass.
[ ] I have updated the documentation accordingly.
[x] I have added tests to cover my changes.
[x] All new and existing tests passed.
[x] All commits have been signed-off for the Developer Certificate of Origin.

Can you please clarify the difference between the pre-merge tests and all new and existing tests? I have passing tests per rake spec && rake style. I didn't see any relevant documentation to update, but if I've missed something please let me know and I'll address it.

chef / knife-cloud