Excessive precision of metrics in losust csv stats

[vstepanov-lohika-tix]

Describe the bug

After upgrade from 0.14.4 to 1.1.1 the most of metrics in csv report became with excessive precision (> 10 digits after point)
It doesn't make sense and makes report hard readable.
Not reproduced in console stats

Expected behavior

Precision for time metrics & content size should be integer number.
Precision for requests rate - float with maximum 2-3 digits after point.

Actual behavior

Over 10 digits after point:

Steps to reproduce

Run any test with HTTP requests & --headless & --csv=report option and check report-stats.csv result file.

Environment

• OS:
• Python version: 3.7.2
• Locust version: 1.1.1
• Locust command line that you ran:
  locust -f {locust_file_path} --headless -u {users_number} -r {hatch_rate} --run-time={run_time} --csv=results --exit-code-on-error=0
• Locust file contents (anonymized if necessary): - complicated.

[heyman]

It seems likely that this was caused by #1428. Previously - when we generated the CSV data manually - we formatted the values using string formatting (%.2f). Now when we're using the built in csv module, we should probably wrap the values in round() calls.

[vstepanov-lohika-tix]

@heyman please take a look draft PR above, will it be ok?

[heyman]

👍👍