Wrap system tables in an *_all version that queries all nodes.

[mponomar]

Makes it easy to fetch, for example, all query fingerprints across the db with a single query.

[akshatsikarwar]

🥇

[mponomar]

Was the medal for the most failing test cases?

[mponomar]

TODO:

• Some deadlock potential when we run SQL from an SQL thread against ourselves - we should uncount our SQL thread at least.
• Fix tests (systables changes break tests, somewhat expected)
• Make sure we're cleaning up correctly (xDisconnect vs xDestroy methods)