Safer one-way kill in close IPC socket test

[Peque]

Hopefully prevents this from happening again:

https://travis-ci.org/opensistemas-hub/osbrain/jobs/341672571

[codecov]

Codecov Report

Merging #251 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #251      +/-   ##
==========================================
+ Coverage   99.08%   99.08%   +<.01%     
==========================================
  Files          26       26              
  Lines        3481     3503      +22     
  Branches      250      251       +1     
==========================================
+ Hits         3449     3471      +22     
  Misses         20       20              
  Partials       12       12

Impacted Files	Coverage Δ
osbrain/helper.py	100% <100%> (ø)	⬆️
osbrain/tests/test_agent_ipc_sockets.py	100% <100%> (ø)	⬆️
osbrain/tests/test_helper.py	100% <100%> (ø)	⬆️

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[ocaballeror]

Looks good.
We should also probably change some of the other tests to use this function instead of arbitrary time.sleep() delays.

[Peque]

@ocaballeror Yeah, I bet there are a couple of tests that could benefit from this. I'll implement the "negated wait_condition()" too in that case and ask you for review again. We can then open a ticket to have a look at where we could use this function.

[Peque]

@ocaballeror Added a negate parameter, which should be useful if we integrate the use of this function in other tests in the near future.