Fixed race condition in registrator.go.

Registrator could miss some Docker events between listing existing containers and starting the event listener. This problem was noted using fig when other containers are starting concurrently with registrator.
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.
Build and package registrator from checkout.

Modified Makefile/Dockerfile to build and package the registrator binary built from the checkout rather than downloading a release from github. This may be more intuitive in that the binary and Docker image created corresponds to the checkout where "make" is run.
Storage backend error logging.

Added error logging to etcd/consul/skydns2 backends so errors are logged to the console while retrying the backend. This helps to show backend problems rather than silently retrying forever.