helperclient.py: factorize request init into mk_request()
helperclient.py: factorize request init into mk_request()

Tanganelli/CoAPthon,mcfreis/CoAPthon,thejdeep/CoAPthon,Gnomjolnir/CoAPthon,Tanganelli/CoAPthon,Gnomjolnir/CoAPthon,thejdeep/CoAPthon