[66139] Ensure Open Model Thread Group initializes config elements only once

[vlsi]

See https://bz.apache.org/bugzilla/show_bug.cgi?id=66139

[codecov-commenter]

Codecov Report

Merging #717 (0a82bc2) into master (7548000) will increase coverage by 0.08%. The diff coverage is 34.61%.

:exclamation: Current head 0a82bc2 differs from pull request most recent head 5de2d3f. Consider uploading reports for the commit 5de2d3f to get more accurate results

@@             Coverage Diff              @@
##             master     #717      +/-   ##
============================================
+ Coverage     55.23%   55.32%   +0.08%     
- Complexity    10381    10393      +12     
============================================
  Files          1062     1062              
  Lines         65760    65763       +3     
  Branches       7533     7534       +1     
============================================
+ Hits          36322    36381      +59     
+ Misses        26837    26777      -60     
- Partials       2601     2605       +4     

Impacted Files	Coverage Δ
...e/jmeter/threads/openmodel/OpenModelThreadGroup.kt	68.53% <0.00%> (+57.17%)	:arrow_up:
.../apache/jmeter/threads/openmodel/scheduleParser.kt	68.93% <0.00%> (-0.68%)	:arrow_down:
...ache/jmeter/threads/openmodel/scheduleTokenizer.kt	79.06% <0.00%> (-1.89%)	:arrow_down:
...org/apache/jmeter/engine/StandardJMeterEngine.java	60.40% <36.36%> (+0.67%)	:arrow_up:
...org/apache/jmeter/threads/AbstractThreadGroup.java	90.14% <50.00%> (ø)
...hreads/openmodel/OpenModelThreadGroupController.kt	100.00% <100.00%> (+75.00%)	:arrow_up:
...jmeter/protocol/http/control/HttpMirrorServer.java	41.41% <0.00%> (-1.02%)	:arrow_down:
...rg/apache/jmeter/threads/JMeterContextService.java	97.82% <0.00%> (+2.17%)	:arrow_up:
...hreads/openmodel/ThreadScheduleProcessGenerator.kt	88.88% <0.00%> (+2.77%)	:arrow_up:
...ache/jmeter/testelement/property/NullProperty.java	65.00% <0.00%> (+10.00%)	:arrow_up:
... and 1 more

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[vlsi]

The test keeps failing at Travis. I'm inclined to disable the test and commit the code.