Test report pipeline API support

[jake-derry]

I need a way to get the test report for a given pipeline. Maybe adding a method in PipelineAPI called getPipelineTestReport would suffice. I'm also willing to work on this issue soon if the main contributors aren't available for it.

[ghilainm]

Would be also interested by this :). Is there anyway to achieve this using the internal GitlabApiClient in the mean time?