CB-7459 Allow automatic tests to be run for specific plugin(s)

Implementation for https://issues.apache.org/jira/browse/CB-7459

See comments in commits for more details.
Nit: Perhaps setupTestsEnabler should accept the testModule directly, and manipulate enabled/disabled and title internally. Also, not all tests will be in the org.apache.cordova namespace (though for Mobilespec they are).

Nit: I think we should rename setupTestsEnabler (not clear what it does by name alone).