Add allow_barman and allow_postgres var for ssh

[klando]

During barman setup, add relevant ssh keys and update known host based on the direction. It is useless as is, but is required later when one want to be able to recover a backup to a server which is not backup by barman: the keys and hosts are known, thus the barman recover command can be used directly.

It's still WIP but I'm working on a role for a stagging server, it requires the ssh direction patch...You may want to wait for this WIP to be proposed before merging this one, up to you.

I have no github fork of this repos thus the pull request the old way with git format-patch.... Sorry for that, and thank you Julien for the merges!

Find git patches here please:

0001-Add-allow_barman-and-allow_postgres-var-for-ssh.tar.gz