Add code coverage to conjur-authn-k8s-client

[andytinkham]

Add code coverage to this project.

Acceptance Criteria:

• Code coverage should be measured across all tests defined in this repository every time a build is run in any branch.
• Coverage report should include:
  • Line Coverage (including highlighting which lines are covered and which are not - not just giving a percentage)
  • Conditional Coverage
  • Optionally, other kinds of coverage such as Package, Class, File, or Method coverage
• Coverage report should be created in or converted to Cobertura format as part of build to allow for ingestion into coverage aggregation tools
• Coverage report should be archived in the Jenkins build using the cobertura command as shown at https://github.com/cyberark/conjur-api-ruby/blob/072d21e01e46382ee4d577e180c1269f8ff9f36e/Jenkinsfile#L27
• Coverage report should be uploaded to Code Climate with each build

[andytinkham]

Coverage is being measured, but there's no way to get the aggregate coverage across the tests. Nothing is loaded to CodeClimate or to the Jenkins build. Building the files that would be sent to those places is difficult because the code is not available to match up with the raw coverage files for each test file.