Allow Google accelerators (i.e. GPUs) on workers

[dghubble]

Warning: This does not magically make GPUs work on Container Linux or Kubernetes. It simply allows advanced users to begin experimenting with them. Like the comments imply, this feature is unofficial, undocumented, unsupported, and may be changed or removed at any time.

Caveats:

• Requires changes to Google Cloud default quotas
• Requires using terraform-provider-google 1.6.0 or higher to work with "0" GPUs properly
• Requires compiling your own kernel modules on Container Linux. (It's possible, I've done it. Just lots of rough edges)
• Some instances will remain un-created forever, because no GPU model is uniformly available across zones and workers are randomized into zones within a region automatically (a Typhoon feature). We just have to fiddle with the count until GCP learns to only try to create the instance in a zone it can actually be created in.

[dghubble]

Mon Mar 12 01:00:04 2018       
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 390.25                 Driver Version: 390.25                    |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|===============================+======================+======================|
|   0  Tesla P100-PCIE...  Off  | 00000000:00:04.0 Off |                    0 |
| N/A   33C    P0    29W / 250W |      0MiB / 16280MiB |      0%      Default |
+-------------------------------+----------------------+----------------------+
                                                                               
+-----------------------------------------------------------------------------+
| Processes:                                                       GPU Memory |
|  GPU       PID   Type   Process name                             Usage      |
|=============================================================================|
|  No running processes found                                                 |
+-----------------------------------------------------------------------------+