Tests: harden test_emcy_consumer_wait

[erlend-aasland]

Wait a little bit longer before dispatching the EMCY packet, and start
the one-shot timer just before invoking the wait() call.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.10%. Comparing base (83594ac) to head (041888c).

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #532   +/-   ##
=======================================
  Coverage   71.10%   71.10%           
=======================================
  Files          26       26           
  Lines        3111     3111           
  Branches      526      526           
=======================================
  Hits         2212     2212           
  Misses        769      769           
  Partials      130      130           

[acolomb]

I'll just run the checks a few times now before merging.

[erlend-aasland]

I'll just run the checks a few times now before merging.

Hold it a little bit; I'd like to also add resource management (joining).