selinux: Print diagnostic message from selinuxd in event on failure

[jhrozek]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

selinuxd does include a diagnostic message for some time and we even
parse it, it was just unused. Instead of changing the CRD just to
include an error message, we might as well just dump the message in an
event.

Which issue(s) this PR fixes:

Fixes #223 (sort of? The issue talked about enhancing the CRD which I
don't think is needed honestly..)

Does this PR have test?

N/A

Special notes for your reviewer:

N/A

Does this PR introduce a user-facing change?

NONE

[codecov-commenter]

Codecov Report

Merging #552 (d97c1e5) into master (7ed53f8) will increase coverage by 0.28%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #552      +/-   ##
==========================================
+ Coverage   43.73%   44.02%   +0.28%     
==========================================
  Files          26       26              
  Lines        1324     1338      +14     
==========================================
+ Hits          579      589      +10     
- Misses        705      709       +4     
  Partials       40       40              

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jhrozek, saschagrunert

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