Rename Debug.FetchVmSettings to Debug.EnableFastTrack

[narrieta]

FetchVmSettings was supposed to be a temporary flag, but there is an actual need for an EnableFastTrack flag so I am renaming it.

Currently EnableFastTrack is in the Debug section, but when Fast Track is released to production it will be moved to the Extensions section.

[codecov]

Codecov Report

Merging #2324 (eb2e5d1) into develop (582d89a) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #2324      +/-   ##
===========================================
+ Coverage    70.74%   70.81%   +0.07%     
===========================================
  Files           97       97              
  Lines        14035    14035              
  Branches      2012     2012              
===========================================
+ Hits          9929     9939      +10     
+ Misses        3660     3654       -6     
+ Partials       446      442       -4     

Impacted Files	Coverage Δ
azurelinuxagent/common/conf.py	77.72% <100.00%> (ø)
azurelinuxagent/common/protocol/wire.py	77.79% <100.00%> (ø)
azurelinuxagent/common/event.py	85.97% <0.00%> (+0.67%)	⬆️
azurelinuxagent/ga/collect_telemetry_events.py	92.12% <0.00%> (+2.39%)	⬆️

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