Starting with requests 2.1.0 non-HTTP scheme URLs are not parsed anymore.
The net effect of this is that when using the unix socket in docker-py no
query string params are passed in the URL. This change makes docker-py
internally use the scheme http+unix to indicate to requests that this is
still a HTTP URL and should be parsed.
Users of docker-py can still specify 'unix:' as the base_url. The
following forms of base_url are accepted.
http+unix://var/run/docker.sock
unix://var/run/docker.sock
unix:///var/run/docker.sock
http://hostname
tcp://hostname