Fix nil panic in Docker error condition
Fix nil panic in Docker error condition

Fixes #2835

Yet another bug caused by overwriting container and then trying to
reference container.ID in the err handling block. Did a quick audit of
docker.go and it seems to be the last offender. See #2804 for previous
bug.

dvusboy/nomad,burdandrei/nomad,Ashald/nomad,nak3/nomad,hashicorp/nomad,burdandrei/nomad,Ashald/nomad,nak3/nomad,dvusboy/nomad,Ashald/nomad,kmalec/nomad,dvusboy/nomad,Ashald/nomad,Ashald/nomad,dvusboy/nomad,frundh/nomad,frundh/nomad,frundh/nomad,nak3/nomad,hashicorp/nomad,kmalec/nomad,Ashald/nomad,frundh/nomad,kmalec/nomad,hashicorp/nomad,dvusboy/nomad,nak3/nomad,Ashald/nomad,dvusboy/nomad,burdandrei/nomad,burdandrei/nomad,nak3/nomad,kmalec/nomad,burdandrei/nomad,hashicorp/nomad,kmalec/nomad,dvusboy/nomad,burdandrei/nomad,nak3/nomad,frundh/nomad,frundh/nomad,hashicorp/nomad,frundh/nomad,burdandrei/nomad,hashicorp/nomad,nak3/nomad,kmalec/nomad,kmalec/nomad