Add v3 of compute rpc API

Add support for the 3.0 compute rpc API.  This commit retains compatibility
with the older 2.X API to allow continuous deployment without any downtime.

The v3 rev of this API was determined primarily by copying the current API
in nova.compute.rpcapi.  That class always reflects the latest rev of the
API that is actually being used.

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

1) Set [upgrade_levels] compute=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-compute service
start sending the new 3.0 messages.

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

Change-Id: I5d303445ded2342a54d8319b79df172ce50fa716
Merge "Add v3 of compute rpc API"