Add option to search for Sonar project by the projectKey

[dschu012]

I am using your plugin in a pipeline and it is having issues finding my master project in Sonar. The repo name is something along the lines of my-repo and the project name in Sonar is My Repo. When using step([$class: 'CompareCoverageAction']) it searches Sonar for http://sonarurl/api/projects/index?search=my-repo and does not find the project (oddly enough if I hit the api with my_repo with an underscore instead of a dash it will find it). It'd be nice if I could do something like step([$class: 'CompareCoverageAction' key: 'my-repo']) hit http://sonarurl/api/projects/index?key=my-repo to find the master project.