4.x: Close sessions properly in DefaultMetadataTabletMapIT

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Moves additional sessions used in this test into try-with-resources statements, ensuring that they are closed afterwards.

Fixes #678.

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I'm not sure why the produced diff looks so utterly confusing, but what this change does is truly just move sessions into variables inside resources sections (and apply formatter).
I have already rebased all my branches.
edit: also the Suppliers in sessions map slightly changed. Each supplier used to create a new session and now it uses a single instance per Supplier instead. If it was important i can roll that back to creating a new instance for each query.

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I see bind exceptions in the logs and that the shard awareness test is still failing (but only for 1 job instead of 3), so maybe it is worth making it less heavy.
Good news is that the change seems to be working because there are no external sessions trying to reconnect to 127.0.18. anymore.

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Rebased on top of scylla-4.x.
See first commit for readable changes without extra indentation.
The hashmap with Suppliers of Sessions is back to how it used to be before the first version of this PR. Added try in a different place instead.