mflags no longer available in upstream docker package

[iamthebot]

Build fails since "github.com/docker/docker/pkg/mflags" is no longer available upstream.

[GongT]

+1

[jasonjayr]

These guys have a fork that can be used.
weaveworks/build-tools#37
weaveworks/weave#2490

[jasonjayr]

#46

Made a quick and dirty pull request for the one-line change.

I've used this project in the past -- is it still required to run docker under systemd ?

[iamthebot]

@jasonjayr it's not required per se (as a workaround, just monitor the docker log command from your systemd unit file) but cgroups support doesn't really work natively with the docker engine yet.