Map unset status code as per spec

[atoulme]

Description:
Maps the UNSET status code according to the spec.
https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/api.md#set-status

Testing:
Unit test

Documentation:
N/A

[codecov]

Codecov Report

Merging #2134 (52ae04e) into master (aab5f2c) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2134      +/-   ##
==========================================
+ Coverage   92.15%   92.16%   +0.01%     
==========================================
  Files         279      279              
  Lines       16983    16983              
==========================================
+ Hits        15650    15652       +2     
+ Misses        913      912       -1     
+ Partials      420      419       -1     

Impacted Files	Coverage Δ
translator/trace/jaeger/traces_to_jaegerproto.go	90.18% <100.00%> (ø)
translator/internaldata/resource_to_oc.go	91.54% <0.00%> (+2.81%)	⬆️

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