Add support for specifying custom SSH port of a managed server

[nstojiljkovic]

This PR adds support for specifying custom SSH port of a managed server. No new configuration option is added, the port should be specified in the existing server configuration option in a standard format, e.g. 192.168.0.1:8022 (for port 8022). It supports IPv6, for example by specifying server to be [::1]:8022. The presented solution is also backwards compatible.

Solution with configuring override.ssh presented in #53 is not optimal when port forwarding is used on a localhost to multiple servers as all of them will share the same internal id in Vagrant.

This closes issue #53.

[pvalena]

LGTM.

[tknerr]

Hey @nstojiljkovic,

first of all, thanks a lot for your PR! 🎉

I'm sorry but I'm currently not finding time to properly support this as needed, also sorry for not getting back to you earlier! :-(

Currently the failing build prevents the merge. But before merging, I would like to (ideally in a separate PR):

1. lift the plugin to be compatible with latest vagrant version
2. fix.travis.yml which is currently failing the build

I will try to find some time during the next days. If you want to support, I'm happy about PRs as well.

Cheers,
Torben