CAD-4707 Pull out common ChainDbArgs from tests

[bartfrenk]

Pull out common ChainDbArgs from tests

Factor out common values for the ChainDbArgs used in various tests, to make it easier to set up new ChainDB tests in the future.

Closes CAD-4707.

Checklist

• Branch
  • [x] Commit sequence broadly makes sense
  • [x] Commits have useful messages
• Pull Request
  • [x] Self-reviewed the diff
  • [x] Useful pull request description at least containing the following information:
    • What does this PR change?
    • Why these changes were needed?
    • How does this affect downstream repositories and/or end-users?
    • Which ticket does this PR close (if any)? If it does, is it linked?
  • [x] Reviewer requested

[bartfrenk]

bors r+

[iohk-bors[bot]]

Build failed:

• ci/hydra:Cardano:ouroboros-network:required

[bartfrenk]

bors r+

[iohk-bors[bot]]

Canceled.

[bartfrenk]

bors r+

[iohk-bors[bot]]

Build failed:

• build (8.10.7, windows-latest)

[bartfrenk]

bors r+

[bartfrenk]

bors r+

[iohk-bors[bot]]

Already running a review

[iohk-bors[bot]]

Build succeeded:

• build (8.10.7, ubuntu-20.04)
• build (8.10.7, windows-latest)
• ci/hydra:Cardano:ouroboros-network:required