Revert "update build_url function in Locust HttpSession "

[vstepanov-lohika-tix]

Reverts #1134
Unfortunately, I've found a big disadvantage of this change:
urljoin from urllib has a surprising behavior: it cuts everything in base url after "/", if the second part of url to join starts from "/".
For example, urljoin("http://mysite.com/api/v0", "/path/to/join")" returns a result: http://mysite.com/path/to/join`

It will lead to a lot of issues and errors in all existing locust tests where combined base url is used.
The only option I see is to revert this change. Sorry for inconvenience.

[codecov]

Codecov Report

Merging #1148 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1148   +/-   ##
=======================================
  Coverage   75.59%   75.59%           
=======================================
  Files          20       20           
  Lines        1881     1881           
  Branches      290      290           
=======================================
  Hits         1422     1422           
  Misses        392      392           
  Partials       67       67

Impacted Files	Coverage Δ
locust/clients.py	91.48% <100%> (ø)	⬆️

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[heyman]

Ah, that's unfortunate. Good that you catched it!