Adds support for secure attribute on token cookie

This patch adds support for the secure attribute on token
cookies (sent by nova-novncproxy). If the https is used
to transfer the cookie, the secure attribute is set thus
restricting server requestes to secure conections only.
This should prevent man-in-the-middle attacks.
Merge pull request #317 from dosaboy/bugs/add_secure_property_to_token_cookie

Adds 'secure' property to 'token' cookie