Add codecov for remaining packages

[mayurkale22]

This PR is an extension of work started here: Codecov: start reporting code coverage. (#232).

Coverage Report available at: https://codecov.io/gh/census-instrumentation/opencensus-node

[codecov-io]

Codecov Report

Merging #251 into master will decrease coverage by 0.84%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #251      +/-   ##
==========================================
- Coverage   95.41%   94.57%   -0.85%     
==========================================
  Files          58      101      +43     
  Lines        3841     7242    +3401     
  Branches      276      681     +405     
==========================================
+ Hits         3665     6849    +3184     
- Misses        176      393     +217

Impacted Files	Coverage Δ
test/test-ocagent.ts	92.99% <0%> (ø)
test/test-instana.ts	100% <0%> (ø)
src/instana.ts	76.27% <0%> (ø)
src/http.ts	88.33% <0%> (ø)
src/validators.ts	100% <0%> (ø)
test/test-zipkin.ts	100% <0%> (ø)
test/test-grpc.ts	99.57% <0%> (ø)
src/ocagent.ts	87.38% <0%> (ø)
src/jaeger.ts	83.14% <0%> (ø)
src/jaeger-driver/index.ts	97.29% <0%> (ø)
... and 33 more

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