Update Log level FATAL and OFF

[jmetertea]

asked first in https://stackoverflow.com/questions/57264142/jmeter-ignore-fatal-off-log-levels

Description

Add OFF/FATAL which is ignored in JMeter documentation although it seems to be working

Motivation and Context

OFF/FATAL is ignored in JMeter documentation although it's working

How Has This Been Tested?

Checked NONE/OFF/FATAL log level and updated accordingly

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.

[codecov-io]

Codecov Report

Merging #547 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #547      +/-   ##
============================================
- Coverage     56.11%   56.11%   -0.01%     
+ Complexity    10020    10019       -1     
============================================
  Files          1024     1024              
  Lines         62910    62910              
  Branches       7064     7064              
============================================
- Hits          35302    35300       -2     
- Misses        25131    25132       +1     
- Partials       2477     2478       +1

Impacted Files	Coverage Δ	Complexity Δ
...a/org/apache/jmeter/timers/PoissonRandomTimer.java	72.97% <0%> (-5.41%)	9% <0%> (-1%)

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[FSchumacher]

Thanks for the patch and the answer on stackoverflow.