I had the same problem. It was triggered by upgrading containerd from 0.2.1~ds1-3 to 0.2.3~git20161117.78.03e5862~ds1-1.
There is an upstream ticket here: https://github.com/docker/containerd/issues/299 I resolved it by downgrading containerd (I found an old copy here: http://ftp.acc.umu.se/mirror/cdimage/snapshot/Debian/pool/main/c/containerd/). It should be fixable by upgrading docker to 1.12 which will pass the socket path in the right format expected by containerd. jamie
