Set Remote.hostname by asking the host itself

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Add Remote.host_key

Turns out we can easily grab the ssh key from paramiko once a connection
is established.

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Add Remote.inventory_info

A property that returns a dict of attributes in the format that the
paddles lock server likes.

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Add lock.update_inventory()

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Add push_inventory() subtask

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Use teuthology.task.internal.push_inventory

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>