Validate the version when running docker version

To avoid unexpected results since docker does a http get to return the
latest version.
For instance, my broadband doesn't return not found when it's down but
a html page saying that the internet is down. Docker is showing that
html instead of ignoring it.

Docker-DCO-1.1-Signed-off-by: Fabio Falci <fabiofalci@gmail.com> (github: fabiofalci)