Add more InstanaExporterHandler tests

[augustjanse]

Four tests for InstanaExporterHandler. These hit four previously uncovered branches in convertToJson(), namely the if statements that check for:

• null status
• Error status
• Multiple spans in a collection
• Multiple attributes in a span

[codecov-io]

Codecov Report

Merging #2014 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #2014      +/-   ##
============================================
- Coverage     83.13%   83.12%   -0.01%     
  Complexity     2250     2250              
============================================
  Files           319      319              
  Lines         10527    10527              
  Branches       1047     1047              
============================================
- Hits           8752     8751       -1     
  Misses         1437     1437              
- Partials        338      339       +1

Impacted Files	Coverage Δ	Complexity Δ
...re/trace/export/InProcessSampledSpanStoreImpl.java	95.85% <0%> (-0.6%)	22% <0%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2903747...92d1419. Read the comment docs.

[songy23]

LGTM