This removes db2 support from tree completely. This is an oddball non
open database that made doing live data migrations difficult. It is
used by 0% of users in the OpenStack User Survey.
Supporting commercial software that doesn't have users at the cost of
delivering features and fixes to our community is the wrong
tradeoff. This corrects that.
It rewrites migrations, which we typically don't ever do, but it is
better if newton fresh environments fail early in db creation instead
of very deep in the data migration process.
Change-Id: Ifeb9929e4515e3483eb65d371126afd7672b92a4
cdf74c57a6