tate: Exclude /var/lib/mysql files from dar backup

The folder backup /var/lib/mysql is ~16gib The db /var/lib/mysql is ~10gib

And the dar backup is ~25gib.

1. i think that backup is redundant with the actual dar system

2. it takes probably more space than needed

3. the space on tate is limited and out of space error seems to cumulate

recently

So makes some room, maybe?

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Migrated from D2471 (view on Phabricator)