kubernetes - add support for surge upgrades

[varshavaradarajan]

Introduce the cluster config option surge_upgrade for users. This will allow the users to choose if they want new worker nodes to be created before destroying the outdated nodes during an upgrade.

[varshavaradarajan]

cc @adamwg, @waynr, @andrewsomething

[andrewsomething]

The change itself looks great, but there are a few more bits that are needed.

The website CI failure is a side effect of the recent repo move. Merging/rebasing on master should resolve it: #468

Though running the acceptance tests, I am also seeing failures. e.g.

    testing.go:640: Step 0 error: Check failed: 1 error occurred:
        	* Check 4/35 error: digitalocean_kubernetes_cluster.foobar: Attribute 'surge_upgrade' expected "true", got "false"

In addition to checking that the value is set, you also need to add surge_upgrade = true to the configs the tests uses.

terraform-provider-digitalocean/digitalocean/resource_digitalocean_kubernetes_cluster_test.go

Line 502 in 20b5ea2

resource "digitalocean_kubernetes_cluster" "foobar" {

terraform-provider-digitalocean/digitalocean/resource_digitalocean_kubernetes_cluster_test.go

Line 544 in 20b5ea2

resource "digitalocean_kubernetes_cluster" "foobar" {

You can run specific acceptance tests using:

make testacc TESTARGS='-run=TestAccDigitalOceanKubernetesCluster_Basic'

Note these do spin up real resources.

We probably also want to set this in the data source:
https://github.com/digitalocean/terraform-provider-digitalocean/blob/master/digitalocean/datasource_digitalocean_kubernetes_cluster.go

And mention it in the docs as well:

https://github.com/digitalocean/terraform-provider-digitalocean/blob/master/website/docs/r/kubernetes_cluster.html.markdown

[varshavaradarajan]

@andrewsomething - thank you for reviewing this. I have addressed your comments. Do you mind taking another look when free?

[andrewsomething]

👍 Looks good, thanks!