* This reverts commit cce4537487.
* Provider passing to child modules is complex and the behavior
changed between Terraform v0.10 and v0.11. We're continuing to
allow both versions so this change should be reverted. For the
time being, those using our internal Terraform modules will have
to be aware of the minimum version for AWS and GCP providers,
there is no good way to do enforcement.
* Allow groups of workers to be defined and joined to
a cluster (i.e. worker pools)
* Move worker resources into a Terraform submodule
* Output variables needed for passing to worker pools
* Add usage docs for AWS worker pools (advanced)
* Set defaults for internal worker module's count,
machine_type, and os_image
* Allow "pools" of homogeneous workers to be created
using the google-cloud/kubernetes/workers module
