code should be updated as indicated in the PR comments  

the following things need to be fixed:

- Not using Runtime.exec as pointed out [here](https://github.com/googleapis/gax-java/pull/1250#discussion_r589861590)
- have foolproof logic for detecting GCE that is able to clearly rule out GAE/GKE so that we don't get false positives as pointed out in this [comment](https://github.com/googleapis/gax-java/pull/1250#discussion_r589861385)