Go15VendorExperiment: Detect go only if vendor includes go files

[forelabs]

I don't think it is necessary to detect Go15VendorExperiment when there are go files in the project but no go files in the vendor folder. We do have this case because we have a little tiny go script in scripts folder but our default vendor rails folder. And there should only be vendor go dependencies if there are go files in the vendor folder I believe.

This adjustment will solve this issue we have in one project and keep the functionality in another where we have go files and a go vendor folder.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this. Unfortunately, the Pivotal Tracker project is private so you may be unable to view the contents of the story.

The labels on this github issue will be updated when the story is started.