Use ssconf port map when handling SSH keys

Use ssconf port map when handling SSH keys

Recently, the SSH port information was added to ssconf
file. This patch makes use of it when adding, removing,
or renewing SSH keys. The main benefit of it is to reduce
the signature of the backend functions and thus the RPC
load.

Signed-off-by: Helga Velroyen <helgav@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>