Retry ssh on Errno::ENETUNREACH

Had issues from Mac OS X with Errno::ENETUNREACH during ```vagrant up --provider=cloudstack``` when connecting to Cloudstack VM's _(with [vagrant-cloudstack](https://github.com/klarna/vagrant-cloudstack) plugin)_.

Similiar the same fix has been used in [puppetlabs-cloud-provisioner](https://github.com/bodepd/puppetlabs-cloud-provisioner) with the fix [retry ssh when Errno::ENETUNREACH is encountered]
(https://github.com/bodepd/puppetlabs-cloud-provisioner/commit/7a239f061d9c59d53b2acc8e2dff5840c18a74c9).