Corrects span StatusCode ordering

[willroberts]

When using opentelemetry and opentelemetry-contrib to report traces to Datadog, I noticed that all spans are marked as errors by default. I was able to correct this by manually calling span.set_status(StatusCode::Ok, ...), but I have since learned that the expectation (which the docs support) is that the default should be Ok instead.

This change updates the ordering to make Ok the default, and updates tests in the Datadog encoder to reflect this change.

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Will (c96ad67, 9a262e1)

[jtescher]

Good catch, thanks!

[codecov]

Codecov Report

Merging #377 (9a262e1) into master (5192fba) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #377      +/-   ##
==========================================
+ Coverage   49.32%   49.34%   +0.01%     
==========================================
  Files          66       66              
  Lines        5326     5326              
==========================================
+ Hits         2627     2628       +1     
+ Misses       2699     2698       -1     

Impacted Files	Coverage Δ
opentelemetry/src/api/trace/span.rs	64.51% <ø> (ø)
...ntelemetry/src/sdk/metrics/aggregators/ddsketch.rs	76.95% <0.00%> (+0.19%)	⬆️

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[willroberts]

I've completed the CLA! Merge at your convenience :)