Add support for setting node pool metadata key/value pairs.

[czka]

No description provided.

[czka]

Should I have squashed my commits?

[morgante]

@czka Do you mind adding some testing for this new parameter? Probably on the node_pool fixture: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/tree/master/test/integration/node_pool/controls

Rebasing is preferred to squashing or merging, but not strongly required.

Thanks for the contribution!

[czka]

@morgante I force-pushed a nice rebased branch for the PR.

Will you not accept my PRs without tests? I looked into that. It's new thing to learn for me and I don't have an easy way to run them myself. I could hack in something I think would be valid, but won't be able to make sure it is. At this moment it's an effort I'd rather avoid, and focus on fixing/extending the module to our needs. This PR (and probably few more in the coming months) is a part of the company I work for evaluating your module as a replacement for their home-grown TF code.

FWIW, an example node_config.*.metadata.shutdown-script might be:

#!/bin/bash -e

kubectl --kubeconfig=/var/lib/kubelet/kubeconfig drain --force=true --ignore-daemonsets=true --delete-local-data $HOSTNAME

[morgante]

@czka We're generally trying to make sure new features have good test coverage. I will see if someone else can add the tests for this, but if not I will merge as is.

[Jberlinsky]

@czka Thank you for your contribution! Like @morgante mentioned, we'd like to add some test coverage to this pull request. Now that we have continuous integration set up, running the tests should be pretty straightforward.

To move this forward, I'm going to merge this pull request into the feature/czka-node-pool-metadata-key-value-pairs branch and add test coverage there. I'll submit a final PR from that branch into master.