Put common import/export daemon options into object

The X509 key name and CA are passed from cmdlib all the way to
the backend import/export daemon. With the addition of an option
to choose the compression method, another parameter would have
to be passed all the way. By moving these options to a separate
object, adding new ones will become much easier.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>