[zaqarclient] limit param of Queue.claim() forward inaccurately to server.

The claim function: Queue.claim() sends the following request message to a server.

-- begin --
POST /v1/queues/{queue_name}/claims
Content-Type: application/json
...

{
    "ttl": {claim_ttl},
    "grace": {message_grace},
    "limit": {limit} <- URL parameter by the specification.
}
-- end --

The message is different from the specification,
   (https://wiki.openstack.org/wiki/Zaqar/specs/api/v1#Claim_Messages)
-- begin --
POST /v1/queues/{queue_name}/claims?limit={limit}
Content-Type: application/json
...

{
    "ttl": {claim_ttl},
    "grace": {message_grace}
}
-- end --