I've also tried working with the QA test on MDLQA-10943. I DID get the drive converter installed, (but only by performing the manual installation and not using the web installer.) Once it was installed, it was displaying debug notices on every page. I just assumed that it was due to a conflict with the "Better Office Integration" project. (also, the code in MDL-58280 seems to be significantly different from the google drive file converter attached to MDLQA-10943)
Hopefully MDL-58280 will make it into Moodle 3.3 eliminating the need for unoconv.