Add V2 rpc api for consoleauth

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

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

    1) Sync all consoleauth services to this commit, so that they handle
       both new and old messages.

    2) Upgrade everything else to this commit so that all clients start
       sending the new messages.

    3) Upgrade past this, where support for the old messages will be
       dropped.

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

Change-Id: Iad71d3c2801f9355968e69bce3308b84f922b239
Merge "Add V2 rpc api for consoleauth"