Previously we were only managing root's known_hosts via ansible but even
then this wasn't happening because the gerrit_self_hostkey var wasn't
set anywhere. On top of that we need to manage multiple known_hosts
because gerrit must recognize itself and all of the gitea servers.
Update the code to take a dict of host key values and add each entry to
known_hosts for both the root and gerrit2 user.
We remove keyscans from tests to ensure that this update is actually
working.
Change-Id: If64c34322f64c1fb63bf2ebdcc04355fff6ebba2
f6a0bf7be5