Allow skipping the logging setup

[Exide]

New CLI option:

--skip-log-setup

This would allow people to setup their own logging configuration. It would also provide a workaround for #163.

[codecov]

Codecov Report

Merging #738 into master will decrease coverage by 0.02%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #738      +/-   ##
==========================================
- Coverage    66.1%   66.08%   -0.03%     
==========================================
  Files          14       14              
  Lines        1422     1424       +2     
  Branches      224      225       +1     
==========================================
+ Hits          940      941       +1     
- Misses        431      432       +1     
  Partials       51       51

Impacted Files	Coverage Δ
locust/main.py	26.38% <33.33%> (+0.22%)	⬆️

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[Exide]

I've not used Codecov before so I'm finding it difficult to understand what threshold I need to meet. Let me know what is needed and I'll rectify it.

[neg3ntropy]

I was trying to use pudb to do some simple debugging, but it fails to open the console interface due to the wrapping of standard error/output

[Exide]

@soulrebel This PR would allow you to skip the call to log.setup_logging which is where that wrapper is established.

[SpencerPinegar]

This should be merged with the code base -- vital when testing code or else the unittestpy.py with error out with -- 'StdOutWrapper' object has no attribute 'getvalue' -- if this functionality could be incorporated into the wrapper that would be cool, but it looked like the getvalue function had other dependencies within the unittestpy.py module.

[aldenpeterson-wf]

This LGTM.

Anyone have objections to me merging this?

[tally38]

Also ran into this issue, and would like this to be merged!