Testing failures in Travis

[stephenplusplus]

See https://travis-ci.org/GoogleCloudPlatform/gcloud-node/jobs/112093216#L2896

In our unit tests, we shouldn't actually be making any gRPC calls, but one or more must be seeping through.

[stephenplusplus]

Now we get:

TypeError: Cannot read property 'currentRetry' of undefined

This might be related to mocha itself. I can't reproduce this locally.