[FIX] Fixed logging using '--log-level'.(maintenance: 617490)

Currently, server is not able to log RPC request/response calls if run with "--log-level"(deprecated) or "--log-handler" option.

Issue can be seen if server started with either of the below parameters,
--log-handler=openerp:DEBUG --log-handler=openerp.http.rpc.request:DEBUG --log-handler=openerp.http.rpc.response:DEBUG
or
--log-level=debug_rpc_answer

or with server config file(used with -c option) having either of the below entries,
log_handler = openerp:DEBUG,openerp.http.rpc.request:DEBUG,openerp.http.rpc.response:DEBUG
or
log_level = debug_rpc_answer

This branch fixes this issue, kindly review it.

Thanks.