remote: change hand written methods to not directly access connection

remote: change hand written methods to not directly access connection

The driver dispatch methods access the priv->conn variables directly.
In future we want to dynamically open the connections for the secondary
driver. Thus we want the methods to call a method to get the connection
handle instead of assuming the private variable is non-NULL.

Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>