This patch creates a new `tlsconfig` package to handle creation of
secure-enough TLS configurations for clients and servers.
The package was created by refactoring TLS code in the client and the
daemon. After this patch, it is expected that all code creating TLS
configurations use this `tlsconfig` package for greater security,
consistency and readability.
On the server side, this fixes a bug where --tlsverify was not taken
into account. Now, if specified, it will require the client to
authenticate.
Signed-off-by: Tibor Vass <tibor@docker.com>
