Vagrantfile - libssh dependency for libnetconf

[alanbarr]

I attempted to spin up a Vagrant VM, but it looks like libnetconf is failing during the configure step, with the following:
configure: error: Missing libssh <>=0.6.4

I'm assuming something similar to this may be required.

I had a crack at it, but it looks like the libssh server is currently out of action - 404 on the tarball.