Added discovery for services running with --net=host.
Added discovery for services running with --net=host.

Containers started with --net=host were not discovered by registrator because their NetworkSettings.Ports section is empty. The corresponding information is however present in HostConfig.PortBindings for containers started using net=host.

This patch adds optional support for HostConfig.PortBindings, but defaults to the configuration in NetworkSettings.Ports to ensure backwards compatibility.

trnubo/registrator,etopian/registrator,leonidlm/registrator,mattrobenolt/registrator,DealerDotCom/registrator,yanndegat/registrator,ch3lo/registrator,disqus/registrator,hostinger/registrator,genki/registrator,rudolfrandal/registrator,mitchcapper/registrator,dotcomputercraft/registrator,42wim/registrator,temskiy/registrator,alderanalytics/registrator,amochtar/registrator,mattaitchison/registrator,kung-foo/registrator,qmsk/registrator,marsmensch/registrator,mulab/registrator,olafnorge/golang-registrator,RobotsAndPencils/registrator,sequenceiq/registrator,temskiy/registrator,gliderlabs/registrator,korjavin/docker-registrator,cptactionhank/graveyard-registrator,clearent/registrator,eBayClassifiedsGroup/registrator,JohnyDays/registrator,42wim/registrator-work,EasonYi/registrator,hudl/registrator,hudl/registrator,lindenlab/registrator,mgood/registrator,bheatwole/registrator,jmeichle/registrator,vimond/registrator,ptklechat/registrator,jgrowl/registrator,asteris-llc/registrator,socrata-platform/registrator,Dexels/registrator,udacity/registrator,lalyos/registrator,wscoble/registrator