In I3e238b6a97769cf0a352f11e718d5d73eebcfa8a, we restored
zzzeek's overlooking the fact that legacy test suites assume
new DBs are provisioned by default in the legacy test base.
However, zzzeek also made this same assumption in Neutron
Ie27cf174fa24c2f479af47335d9ae139fb7d159a which vendors its
own version of test_base in anticipation of some of these newer
features, so it will break once the provision_new_database flag
becomes false. Favor setting this flag True/False explicitly
and default it to True for compatibility w/ Neutron.
Change-Id: I726cc20481a9bc778b75564526d9245132b43563