Fetching the Google credentials is done before attempting to upload APKs from the workspace.

Which means that this is done on the master, rather than on the build agent, so the plugin doesn't work in setups where the master does not have internet connectivity, but the agents do.

Ideally, we should do all network operations on the same machine.

To check:
1. That this works for all types of operations (i.e. also when doing track assignment from an agent, with/without APKs to read the versionCodes from)
2. What happens on the master when configuring a job, but there's no internet connectivity (AFAIR, we attempt to verify the credentials at job config time)