Fix empty bytearray(b'') returned when using catch_response=True

[skivis]

This is a potential fix for a bug that causes the content to be "dropped" when passing catch_response=True in combination with FastHttpLocust.

To recreate, run following locust-file with locust v0.12.0:

from locust import TaskSet, task
from locust.contrib.fasthttp import FastHttpLocust


class ExamplePage(TaskSet):
    @task
    def index(self):
        with self.client.get("/", catch_response=True) as r:
            print(r.content)


class AwesomeUser(FastHttpLocust):
    task_set = ExamplePage
    host = "http://example.com"

Inside ResponseContextManager.__init__ the responses __dict__ is copied over, but for some reason the content doesn't tag along...

To be honest, I'm still not entirely sure why it gets dropped, might even be something in geventhttpclient but this fixes the issue and seems unobtrusive enough.

Please have a look, if anyone has a better solution, I'm all ears :)

[codecov]

Codecov Report

Merging #1105 into master will increase coverage by 0.19%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1105      +/-   ##
==========================================
+ Coverage   72.29%   72.48%   +0.19%     
==========================================
  Files          17       17              
  Lines        1700     1701       +1     
  Branches      253      253              
==========================================
+ Hits         1229     1233       +4     
+ Misses        408      406       -2     
+ Partials       63       62       -1

Impacted Files	Coverage Δ
locust/contrib/fasthttp.py	92.21% <100%> (+0.04%)	⬆️
locust/core.py	86.3% <0%> (+1.36%)	⬆️

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[heyman]

Nice catch (pun intended) :)!

[tovalepo]

I'm using locust V1.3.1, where this solution is already implementd. However I'm still getting an empty bytearray (b") when calling a GET endpoint.
I tested the REST via Postman, and the response returns as required.
Any clue?