qapi: allow blockdev-add for ssh

Introduce new object 'BlockdevOptionsSsh' in qapi/block-core.json to
support blockdev-add for SSH network protocol driver. Use only 'struct
InetSocketAddress' since SSH only supports connection over TCP.

Signed-off-by: Ashijeet Acharya <ashijeetacharya@gmail.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
[ kwolf: Removed host_key_check option, we want to expose this later in
  a structured way rather than as a string that must be parsed ]
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
