libvirt: Convert more tests to use instance objects

Convert a bunch more test cases over to use objects.Instance
instead of a dict()

Blueprint: libvirt-driver-class-refactor
Change-Id: I4f34c9c795f99e56dd6ca27be237e8c2252f782e
Only check db/api.py for session in arguments

We were checking both db/api.py and db/sqlalchemy/api.py for session
in db apis, but db apis are only defined externall in db/api.py. This
rule will falsely match on non-api methods in db/sqlalchemy/api.py
which take a session argument. Passing the session around within this
module is considered a good thing.

Change-Id: Ibf5d1284b44013c736b6b70ca4fa5d706c365c7d
fix import of oslo.concurrency

It's now oslo_concurrency, and importing the old symbol triggers a
deprecation warning. There were 2 instances of this unfixed.

Change-Id: Ib63da2d845843410634a1df0261af33b973daf32
Merge "fix import of oslo.concurrency"
Merge "libvirt: Convert more tests to use instance objects"
Merge "Only check db/api.py for session in arguments"