R1:917da084176c

Fix various MySQL version issues with new charset stuff

Summary:
Ref T1191. Notable stuff:

- Adds `--disable-utf8mb4` to `bin/storage` to make it easier to test what things will (approximately) do on old MySQL. This isn't 100% perfect but should catch all the major stuff. It basically makes us pretend the server is an old server.
- Require utf8mb4 to dump a quickstart.
- Fix some issues with quickstart generation, notably special casing the FULLTEXT handling.
- Add an `--unsafe` flag to…