Device mapper was creating an invalid cgroup name.

This was breaking docker top CONTAINER

Docker-DCO-1.1-Signed-off-by: Daniel Walsh <dwalsh@redhat.com> (github: rhatdan)
This check was backwards.

If I do a

docker events  > /tmp/out

I do not want the control characters getting written to the file.
The check should check the output file not the input file.

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)