Add a get method to retrieve the SSH public key contents.

[mykaul]

This will be used later to install hosts using public key, for Ansible, etc.

[mykaul]

Not good enough. I need the fingerprint retrieved as well. ARGH. Don't merge yet.

[mykaul]

Might be good enough (so I can later add in ovirt-system-tests a test that adds a User with SSH Public Key). If there are no comments, I'd be happy to get it in.
(For host-based SSH PK installation, I'll need the fingerprint. This will need to be worked on differently - I assume running some command on the Engine).