Fixed broken vncproxy flush tokens patch

Bug 1125378 (continued)

This review (https://review.openstack.org/22872) attempted to
resolve a critical security issue but ended up completely breaking
the vncproxy. The wrong dict keys were being used for Essex and the
API calls were incomplete. This patch makes the proxy work again.

Change-Id: I093d522abd5be20d2792c83792437b1ef580d4c6
Merge "Fixed broken vncproxy flush tokens patch" into stable/essex