pkg/trace/agent: ensure normalizer reports bad service name

[gbbr]

This change ensure that the normalizer reports a bad service name.
Previously it would always report the empty string on error.

[ufoot]

Yup this is better, as a side note I think resource has a similar behavior:

https://github.com/DataDog/datadog-agent/pull/2942/files#diff-4140e394b1bfca821a710b030200a141R64

[gbbr]

@ufoot you're right. I've made that change. Please re-approve.

[codecov-io]

Codecov Report

Merging #2942 into master will decrease coverage by 0.36%.
The diff coverage is 63.63%.

@@            Coverage Diff             @@
##           master    #2942      +/-   ##
==========================================
- Coverage   56.38%   56.02%   -0.37%     
==========================================
  Files         482      441      -41     
  Lines       34169    27280    -6889     
==========================================
- Hits        19267    15283    -3984     
+ Misses      13744    10965    -2779     
+ Partials     1158     1032     -126

Impacted Files	Coverage Δ
pkg/trace/agent/normalizer.go	82.6% <63.63%> (-1.06%)	⬇️
pkg/collector/runner/runner.go	53.15% <0%> (-13.87%)	⬇️
pkg/trace/sampler/prioritysampler.go	49.05% <0%> (-11.99%)	⬇️
pkg/metadata/resources/resources.go	75% <0%> (-8.34%)	⬇️
pkg/trace/sampler/scoresampler.go	58.33% <0%> (-7.71%)	⬇️
pkg/quantile/key.go	46.15% <0%> (-7.18%)	⬇️
pkg/trace/api/listener.go	52% <0%> (-5.9%)	⬇️
pkg/util/kubernetes/clustername/clustername.go	57.89% <0%> (-5.75%)	⬇️
pkg/procmatch/signature.go	66.66% <0%> (-4.77%)	⬇️
pkg/metrics/event.go	67.1% <0%> (-4.64%)	⬇️
... and 327 more

[ufoot]

Thanks for making this more reliable.

[ufoot]

good catch !