Fix Python 3.8, SQLAlchemy 1.4 and MySQL 8 (backport #1147) (backport #1151)

[mergify]

This is an automatic backport of pull request #1151 done by Mergify.
Cherry-pick of 58c78bf has failed:

On branch mergify/bp/stable/4.3/pr-1151
Your branch is ahead of 'origin/stable/4.3' by 2 commits.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit 58c78bf0.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   gnocchi/indexer/sqlalchemy.py
	modified:   gnocchi/indexer/sqlalchemy_base.py

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   gnocchi/amqp1d.py

Cherry-pick of 4d2e0d9 has failed:

On branch mergify/bp/stable/4.3/pr-1151
Your branch is ahead of 'origin/stable/4.3' by 3 commits.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit 4d2e0d91.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   tox.ini

no changes added to commit (use "git add" and/or "git commit -a")

Cherry-pick of 2b01ed1 has failed:

On branch mergify/bp/stable/4.3/pr-1151
Your branch is ahead of 'origin/stable/4.3' by 7 commits.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit 2b01ed1b.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   gnocchi/amqp1d.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   gnocchi/tests/test_storage.py
	both modified:   tox.ini

To fix up this pull request, you can check it out locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

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