Just tripped into that one: I upgraded a Rancher host to 0.4.5, rebooted it & somehow only the system-docker daemon came up.

The user facing container was stuck in a reboot loop:

CONTAINER ID        IMAGE                       COMMAND                  CREATED             STATUS                          PORTS               NAMES
e11da889990c        rancher/os-docker:v0.4.5    "/usr/sbin/entry.sh /"   11 minutes ago      Restarting (0) 47 seconds ago                       docker
9f0f66b8eef0        rancher/os-console:v0.4.5   "/usr/sbin/entry.sh /"   11 minutes ago      Up 11 minutes                                       console
cbe4d0a044a7        rancher/os-network:v0.4.5   "/usr/sbin/entry.sh /"   13 minutes ago      Up 13 minutes                                       network
d9da62a858d4        rancher/os-ntp:v0.4.5       "/usr/sbin/entry.sh /"   13 minutes ago      Up 13 minutes                                       ntp
dc4b0f37cd86        rancher/os-udev:v0.4.5      "/usr/sbin/entry.sh /"   13 minutes ago      Up 13 minutes                                       udev
e932a592abf3        rancher/os-acpid:v0.4.5     "/usr/sbin/entry.sh /"   13 minutes ago      Up 13 minutes                                       acpid
c866fe780221        rancher/os-syslog:v0.4.5    "/usr/sbin/entry.sh /"   13 minutes ago      Up 13 minutes                                       syslog

Check your /var/log/docker.log see if you are running into #18283:

Error starting daemon: Error initializing network controller: could not delete the default bridge network: network bridge has active endpoints.

The solution was fairly easy:

$ sudo rm -r /var/lib/docker/network; sudo reboot;