Add code coverage for cloudfoundry-conjur-buildpack

[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