Adding this functionality required the existing DNS api
to be rearranged considerably.
Nova needs to track some information about domains that is
outside the scope of the DNS driver, specifically the availability
zone of a private domain and the project of a public domain.
In order to track those attributes, this patch adds a new table
to the Nova database, dns_domains.
This patch perpetuates some naming ambiguities (e.g. zone vs. domain).
A future renaming patch will sort all this out.
For blueprint public-and-private-dns.
Change-Id: I80865207d34ab7c6e2afc5638863a299b3913f8e
92e66df6e7