More consistently pass --package-db flag to tests (backport #9954) (#10067)

* More consistently pass --package-db flag to tests

Previously `--package-db` was only passed to test which used the `v2-`
prefix.

Now we pass `--package-db` to things which use the `v2-` prefix, not
things which use the `v1-` prefix and by default assume that unprefixed
commands are v2 commands.

(cherry picked from commit 2b44677c)

# Conflicts:
#	cabal-testsuite/PackageTests/CustomTestCoverage/cabal.out

* fixup! resolve conflicts

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Co-authored-by: Matthew Pickering <matthewtpickering@gmail.com>
Co-authored-by: Artem Pelenitsyn <a.pelenitsyn@gmail.com>