Add V2 rpc api for console

Add support for the 2.0 console rpc API.  This commit retains compatibility
with the older 1.X API to allow continuous deployment without any downtime.

The v2 rev of this API is really simple.  It removes the
get_backdoor_port() method, which was moved to the base rpc API common
to all services in havana.  It also removes some unused parameters.

UpgradeImpact - Deployments doing continuous deployment should follow this
process to upgrade without any downtime with the consoleauth service:

1) Set [upgrade_levels] console=havana in your config.

2) Upgrade to this commit.

3) Once everything has been upgraded, remove the entry in
[upgrade_levels] so that all rpc clients to the nova-console service
start sending the new 2.0 messages.

Part of blueprint rpc-major-version-updates-icehouse

Change-Id: If05d041c5104b7f4e2e6b035de33cdd695c7a1ae
Merge "Add V2 rpc api for console"