Adds support for Nova RDP console

Hyper-V employs RDP to access virtual machine consoles, unlike most
other hypervisors which support VNC.

In order to support this scenario, the get_rdp_console API has been
added to Nova. This commit adds the corresponding UI feature,
implemented in a way consistent with existing VNC and SPICE console
support.

Change-Id: I9722a1aef5d26184f5a6bc278e306acbdae76b7b
Blueprint: hyper-v-rdp-console
Merge "Adds support for Nova RDP console"