Allow setting node locations on individual node pools

[morgante]

As added upstream, we need to update this module to support specifying node_locations on individual node pools (that potentially differ from the cluster's overall locations).

This will unblock #263.

[bharathkkb]

@morgante I can pick this up next if no one else has started

[morgante]

@bharathkkb Go ahead, thanks!

[bharathkkb]

@morgante quick question about this. I was trying to implement it like below but seems like I cant have arrays and strings within a single map.

node_pools = [
   {
      name               = "my-node-pool"
      node_locations     = ["us-west1-a", "us-west1-c"]
      .....
    }]

For taints, tags etc which requires lists we have used a different variable. Should I use that approach here?

node_pools = [
    {
      name               = "my-node-pool"
      .....
    }]
  node_pools_locations={
      my-node-pool = ["us-west1-a", "us-west1-c"]
    }

[morgante]

I'd suggest we simply comma-separate the locations in a string, as the simplest approach.

[bharathkkb]

Yes that makes sense. Thanks

[aaron-lane]

By the by, I've opened #306 to address the limitation of node_pools using maps rather than objects.