Use new Jenkins Code Coverage API Plugin

[thomas-riccardi]

See:

• https://plugins.jenkins.io/code-coverage-api/
• https://www.jenkins.io/doc/pipeline/steps/code-coverage-api/
• https://github.com/jenkinsci/code-coverage-api-plugin/wiki
• https://www.jenkins.io/blog/2018/08/17/code-coverage-api-plugin-1/

Why?

• more modern, code coverage unification
• It allows us to handle more formats than just cobertura (plugin-based).
• PR coverage diff
• more explorable coverage trend
• finer-grained reports grouping (we could do per dmake service, or per group of services with extra dmake.yml config, using plugin "tag" feature)
• finer-grained success thresholds (we could fail the build for low coverage for one report and accept a lower coverage in another report)

[thomas-riccardi]

v1

See #446:

• publish both on old and new plugin, no change to dmake.yml

v1.1

• diff with target branch doesn't work well with "build only changed services" feature. Maybe fix that with tags/groups reports ?

v2

• remove old coberturaPublisher
• add new code_coverage section in dmake.yml to replace cobertura
  • add options to control failure thresholds, reports grouping, etc..
• collect reports ASAP: we'll get partial results before the end of the build
  • related: maybe try to fix #374 for at least this coverage collect?
• try to collect source files: tricky part: 3 base paths: in container when generating report; root workspace host path (or current path?); report host path (.dmake/<uuid>/*...), see https://github.com/jenkinsci/code-coverage-api-plugin/issues/159

[thomas-riccardi]

coverage diff publish on github is not planned for now: all 2 plugins that do such things are reimplementing xml parsing instead of working on top of code-coverage-api-plugin...

[thomas-riccardi]

skipped to v3: Code Coverage Plugin is deprecated, use now Coverage Plugin, cf #569