BUG/MINOR: httpclient/lua: rcv freeze when no request payload

BUG/MINOR: httpclient/lua: rcv freeze when no request payload

This patch fixes the receive part of the lua httpclient when no payload
was sent.

The lua task was not awoken once it jumped into
hlua_httpclient_rcv_yield(), which caused the lua client to freeze.

It works with a payload because the payload push is doing the wakeup.

A change in the state machine of the IO handler is also require to
achieve correctly the change from the REQ state to the RES state, it has
to detect if there is the right EOM flag in the request.