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ARROW-5217: [Rust] [DataFusion] Fix failing tests

Due to recent changes in the HashMap implementation in Rust nightly, some non-deterministic tests started failing. This is a quick PR to fix this. It also seems that there are changes to `cargo fmt` so there are formatting changes in this PR too.

I commented out `csv_query_group_by_avg_multi_batch` for now as there is something more complex causing that one to fail. I can look at that over the weekend.

Author: Andy Grove <andygrove73@gmail.com>

Closes #4217 from andygrove/ARROW-5217 and squashes the following commits:

ad2bccaa <Andy Grove> fix build