Change default TLS version
Change default TLS version

Detects if python has an up-to-date version of OpenSSL that supports
TLSv1.2. If it does, choose that as the default TLS version, instead of
TLSv1. The Docker Engine and the majority of other Docker API servers
should suppot TLSv1.2, and if they do not, the user can manually set a
different (lower) version.

Signed-off-by: Drew Erny <83d780db39fae693cf18623ace93c7ec0dc91590@docker.com>

docker/docker-py,funkyfuture/docker-py,vdemeester/docker-py,funkyfuture/docker-py,vdemeester/docker-py,youhong316/docker-py,youhong316/docker-py,docker/docker-py