Adds support for the get_rdp_console API

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 client side feature,
implemented in a way consistent with existing VNC and SPICE console
support.

Nova Gerrit commit: https://review.openstack.org/#/c/43502/

Change-Id: I86b814797d234f1eb49a7fa67ed27a9bcda034ae
Implements: blueprint hyper-v-rdp-console
Merge "Adds support for the get_rdp_console API"