Fix TLS events

Event monitoring is not working under TLS because it isn't using Client.HTTPClient. This patch fixes it.

Includes a test using TLS mutual authentication. Probably needs some negative testing (e.g connecting HTTP client to HTTPS server or vice versa) to better validate error handling.
I'm totally fine with 2376 => https as the default.  The issue is that since the docker daemon allows the user to pass `-H` with whatever option they want, on any machine that's not `boot2docker`, the user may be using a different port.  I'd hate for somebody to have to change the settings of their docker daemon (and reboot it!) just to use the go-dockerclient