VNC console does not work with VCDriver

Introduces get_vnc_console_vcenter as a way to get
a modified vnc_console object that connects to the
ESXi host underneath vCenter control.

* adds new fake classes for testing
* documents classes, methods & API logic

fixes bug: #1178369

Change-Id: I48430cb9bc9615e02ca9af235f97853f3f0bdafd