Fixes setup.cfg, adding current exclude rules, simplified tox.ini to use
setup.cfg and fixed all.

If we create all at once we cant test higher loads because it will try
to hold all in memory at the same time. Also, this code is smaller and
more readable.

It's not being used

Temporary fix for server streaming

We were using 'x'*size as payload, but on real usage the payload will be
random. This commit randomizes the payload using a predefined seed, so
the random payload will be the same across benchmarks.
Using random payloads also improves accuracy of compression or encoding
impacts and we will be evaluating those changes for resouce usage
issues.
Also note that base64 is used on payload. That was needed for utf8
safety, but overhead was removed to leave payloads as defined by
benchmarks.
Base64 was chosen also due its popular usage on MIME encoding, which is
used on mail attachments (our current scenario).

They arent used so far and using empty dicts to make them work is ugly.
Removing it leaves the return function on setup code clean and readable.

Syncing without any changes was reported as slow. This benchmark will
help measure it.

If we have many scenarios (like 20/500k, 100/100k, 1000,10k) then making
a nested function to generate tests based on scenario parameters
simplifies the code a lot.