If the required extensions are missing, we currently log an error
that is going to be practically ignored. That said, the unfulfilled
requirement will most definitely going to lead to other failures,
so we might as well fail fast.
This patch also cleans up some <barf>dns-integration nonsense</barf>
within the ML2 framework: the extension must not be declared statically
as it's being loaded by the extension manager, and this fixes the lousy
unit tests we have to live with. As for the db base plugin, some cleanup
is still overdue, but it will have to be taken care of in a follow-up
patch.
Closes-bug: #1538623
Change-Id: Id50eeb52c5d209170042b48821a29af3421c2f5c
b14c06b5ed