Add checker test for bad pid

[antoineco]

What this PR does / why we need it:

The second "valid request" checker test makes little sense because the pid file is rewritten with the expected pid. I adapted it to ensure we also fail in case the process with the expected pid does not exist.

/assign @aledbf

[aledbf]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, antoineco

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[aledbf]

@antoineco thanks!

[codecov-io]

Codecov Report

Merging #2191 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #2191   +/-   ##
======================================
  Coverage    36.4%   36.4%           
======================================
  Files          69      69           
  Lines        4859    4859           
======================================
  Hits         1769    1769           
  Misses       2820    2820           
  Partials      270     270

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