[FLINK-22462][jdbc] Fix connection leak and stabilize JdbcExactlyOnceSinkE2eTest

[rkhachatryan]

1. Close pooled and physical connections in XaFacadeImpl (tolerate close errors for MySQL)
2. Harden test by adding MySql
3. Prevent sources from waiting on cancellation
4. Prevent sources from using a latch from a different attempt

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[curcur]

Let's sync up offline?

1. what causes the job to have more than 200 connections, with parallelism = 4?
2. If we have too many connections for the preparing state(uncommitted), can we slow down the source pace?
3. Should we set up an upper limit for connection pool size?
4. Why "Prevent sources from waiting on cancellation" would help to reduce the connection in this case?

[rkhachatryan]

Thanks for reviewing the PR @curcur.
I've addressed your concerns and also updated production code (so there is no connection issue now); and added MySQL setup, PTAL.

[AHeise]

Thank you very much the fix and the extended test. A quick question: shouldn't we reorder the commits such that the fix appears before the test?

[rkhachatryan]

I agree, reordered the commits and rebased them onto the latest master.