[DPE-4173] Miscellaneous improvements to continue stabilizing exporter integration tests (#254)

## Issue
1. We are using connection pools in our exporter integration tests. As
these connection pools use connections with keep-alive, the guess is
that the server has connections in `TIME_WAIT` for a period of time when
it shuts down. Immediately starting the server (in consecutive tests)
results in `bind-address in use` error
2. We are running to 2 possibly flakey tests back to back (the first one
unrelating and the second one shortly relating with COS right after)

## Solution
1. Use `requests.get(stream=False)` instead of using connection pools
2. Split the 2 tests into separate files so that they are part of
separate groups and run separately

## Notes
Tests passed in 1 retry compared to usually higher retries

Author: shayancanonical