The mentality of being able to continuously deliver nova
has been around since the beginning with Rackspace public
cloud trying to CD openstack as close to master as possible.
This has implications for how code series are structured,
reviewed and merged. For the most part this seems to be tribal
knowledge and we don't have anything very obvious in the nova
docs about it, and not all projects in openstack necessarily
subscribe to this mentality anymore, or do so grudgingly, but
it's worth documenting it in nova while still applied here.
Change-Id: Ieff87dbd748318f1b7f879a136ff25081dac321e
e619354f7c