Port certificates API to v3 Part 1

This changeset only copies the v2 files (implementation and test)
into the appropriate v3 directories unchanged. The copy as-is
will not be loaded by either the v2 or v3 extension loaders. The
second changeset will then make the changes required for it to
work as a v3 extension.

This is being done in order to make reviewing of extension porting
easier as gerrit will display only what is actually changed for v3
rather than entirely new files

Partially implements blueprint nova-v3-api

Change-Id: Ibdb3b444432fa707786e6bb43aaba61d2a3fc89f
Revert "Add oslo-config-1.2.0a2 and pbr>=0.5.16 to requirements."

This partially reverts commit:
   43b7f22b30244114f809e4c3b44dc337cade95f1.

The oslo.config change in that patch seems to break running unit
tests with tox. This reverts just that part of the change.

Change-Id: I977700d73342e81ee962019b76238d2cb2b1fff4
Merge "Port certificates API to v3 Part 1"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp