Stop using ssh_authorized_key with a fixed name,
and move key generation to a template. It will accept
an ssh_key parameter, that can accept either an array
or a single string. And it will populate these keys on the
.ssh/authorized_keys properly.
Doing that we allow to rotate keys properly, and avoid
some of the races that could be originated using a
single key using the ssh_authorized_key way.
Change-Id: I572b7a18186329c4277a3f460fc05e6eb30c63b7
a22f8d8500