RUST-1627: Add automatic token acquisition for GCP

[pmeredit]

So, the tests here look quite weird. The GCP VM is incredibly slow, so I wasn't able to run cargo test on it. I tried, it took over 2 hours to compile the mongodb crate and timed out. So the strategy here is to statically compile the test, tar it up, and run the binary. The VM doesn't even have the correct version of libc, which necessitates fully statically compiled test app. Since this worked, I went ahead and changed Azure to this too, since it also runs on a VM, which more than halved the runtime for the Azure test. I'm not sure why the Azure VM is so much snappier than the GCP VM, but it is what it is.