Fix percentiles printed in _stats.csv file

[mehta-ankit]

Describe the bug

Using --csv flag in 0.13.3 version of locust (after #1146 was merged) only prints percentiles in the sliding window of CURRENT_RESPONSE_TIME_PERCENTILE_WINDOW. This happened because instead of using get_response_time_percentile i added get_current_response_time_percentile to requests_csv function.

Expected behavior

The percentiles printed in this file should be percentiles over the test run duration instead of over the last sliding window duration (which is 10 seconds as default). Since we anyways get the granularity of each interval of stats entries in _stats_history.csv with the --csv--full-history flag.

Actual behavior

The percentiles printed are for only the last 10 seconds of the test run. Since this file is overwritten at every interval using get_current_response_time_percentile() function only gives us that last duration percentiles.

Steps to reproduce

Run a locust test using --csv flag and look at the _stats.csv file.

Environment settings

• OS: Mac OSX 10.14.6 (Terminal info: Darwin Kernel Version 18.7.0)
• Python version: 3.7.4
• Locust version: 0.13.3

[mehta-ankit]

This PR fixes the issue: #1197