Detect WebMock to disable telemetry and remote configuration

[TonyCTHsu]

What does this PR do?

It has been reported by the community that ddtrace is breaking test suite with WebMock, since some components are sending http request in the background with net/http .

Hence this PR make an effort the detect WebMock to provide a better default value for ddtrace telemetry and remote configuration.

WebMock does not offer an public API such as WebMock.enabled? to check the status. When WebMock.enable!, it iterates through http adapters to enable them. The net/http adapter implements enablement by swapping the reference for Net::HTTP

[codecov-commenter]

Codecov Report

Merging #3065 (188f7db) into master (737db7b) will decrease coverage by 0.01%.
Report is 34 commits behind head on master.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3065      +/-   ##
==========================================
- Coverage   98.15%   98.15%   -0.01%     
==========================================
  Files        1323     1323              
  Lines       75089    75134      +45     
  Branches     3424     3424              
==========================================
+ Hits        73704    73746      +42     
- Misses       1385     1388       +3     

Files Changed	Coverage Δ
lib/datadog/core/environment/execution.rb	100.00% <100.00%> (ø)
spec/datadog/core/environment/execution_spec.rb	95.45% <100.00%> (+3.96%)	⬆️

... and 2 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more