Also run v2 functional tests with registry

Currently the v2 functional tests are run without the v2 registry enabled.

This means that bugs which are only seen when the v2 registry is enabled
may not be caught by the gate (eg #1308419, #1339775).

Here we enable some basic functional testing (eg image life cycle) with
the v2 registry enabled (in addition to the existing direct-to-database
mode). This should help prevent some types of bugs being introduced.

There is a plan to move some functional tests into tempest, at which
point these additional tests can be removed in favour of equivalent
tempest tests.

Change-Id: I774a277673390650874aad4334b28d1a872ea93f
Merge "Also run v2 functional tests with registry"