Allow version: auto in the config file when creating a cluster

[martina-if]

This allows the version to have the value auto when creating a cluster. This value
was only supported when creating a nodegroup and upgrading a cluster. Now it can also
be used when creating a cluster. In this case, eksctl will use the default version.

eksctl create cluster

$ eksctl create cluster -f examples/01-simple-cluster.yaml 
[ℹ]  eksctl version 0.26.0-dev+307fe94b.2020-08-03T16:51:48Z
[ℹ]  using region eu-north-1
[ℹ]  setting availability zones to [eu-north-1b eu-north-1a eu-north-1c]
[ℹ]  subnets for eu-north-1b - public:192.168.0.0/19 private:192.168.96.0/19
[ℹ]  subnets for eu-north-1a - public:192.168.32.0/19 private:192.168.128.0/19
[ℹ]  subnets for eu-north-1c - public:192.168.64.0/19 private:192.168.160.0/19
[ℹ]  nodegroup "ng-1" will use "ami-043dbb11ff9b5a350" [AmazonLinux2/1.17]
[ℹ]  using Kubernetes version 1.17
...
[ℹ]  nodegroup "ng-1" has 1 node(s)
[ℹ]  node "ip-192-168-83-103.eu-north-1.compute.internal" is ready
[ℹ]  kubectl command should work with "/home/martina/.kube/config", try 'kubectl get nodes'
[✔]  EKS cluster "martina-test-auto-1" in "eu-north-1" region is ready

eksctl create nodegroup

$ cat test.yaml 
---
apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig

metadata:
  name: martina-1-13-2
  region: eu-north-1
  version: "auto"

nodeGroups:
  - name: ng-2
    instanceType: t3.medium
    desiredCapacity: 1

$ eksctl create nodegroup -f test.yaml --include ng-2
[ℹ]  eksctl version 0.26.0-dev+307fe94b.2020-08-03T16:51:48Z
[ℹ]  using region eu-north-1
[ℹ]  will use version 1.13 for new nodegroup(s) based on control plane version
[ℹ]  nodegroup "ng-2" present in the given config, but missing in the cluster
[ℹ]  nodegroup "ng-84dc9dc0" present in the cluster, but missing from the given config
[ℹ]  1 existing nodegroup(s) (ng-84dc9dc0) will be excluded
[ℹ]  nodegroup "ng-2" will use "ami-046b83e67325d4d1e" [AmazonLinux2/1.13]
[ℹ]  combined include rules: ng-2
[ℹ]  1 nodegroup (ng-2) was included (based on the include/exclude rules)
[ℹ]  will create a CloudFormation stack for each of 1 nodegroups in cluster "martina-1-13-2"
[ℹ]  1 task: { 1 task: { 1 task: { create nodegroup "ng-2" } } }
[ℹ]  building nodegroup stack "eksctl-martina-1-13-2-nodegroup-ng-2"
[ℹ]  --nodes-min=1 was set automatically for nodegroup ng-2
[ℹ]  --nodes-max=1 was set automatically for nodegroup ng-2
[ℹ]  deploying stack "eksctl-martina-1-13-2-nodegroup-ng-2"
[ℹ]  no tasks
[ℹ]  adding identity "arn:aws:iam::123:role/eksctl-martina-1-13-2-nodegroup-n-NodeInstanceRole-1U3IUW46A2KTN" to auth ConfigMap
[ℹ]  nodegroup "ng-2" has 0 node(s)
[ℹ]  waiting for at least 1 node(s) to become ready in "ng-2"
[ℹ]  nodegroup "ng-2" has 1 node(s)
[ℹ]  node "ip-192-168-53-160.eu-north-1.compute.internal" is ready
[✔]  created 1 nodegroup(s) in cluster "martina-1-13-2"
[✔]  created 0 managed nodegroup(s) in cluster "martina-1-13-2"
[ℹ]  checking security group configuration for all nodegroups
[ℹ]  all nodegroups have up-to-date configuration

eksctl upgrade cluster

$ cat test.yaml 
---
apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig

metadata:
  name: martina-1-13-2
  region: eu-north-1
  version: "auto"

nodeGroups:
  - name: ng-2
    instanceType: t3.medium
    desiredCapacity: 1

$ eksctl upgrade cluster -f test.yaml 
[ℹ]  eksctl version 0.26.0-dev+307fe94b.2020-08-03T16:51:48Z
[ℹ]  using region eu-north-1
[!]  NOTE: cluster VPC (subnets, routing & NAT Gateway) configuration changes are not yet implemented
[ℹ]  (plan) would upgrade cluster "martina-1-13-2" control plane from current version "1.13" to "1.14"
[ℹ]  re-building cluster stack "eksctl-martina-1-13-2-cluster"
[ℹ]  (plan) updating stack to add new resources [PolicyELBPermissions] and outputs []
[ℹ]  checking security group configuration for all nodegroups
[ℹ]  all nodegroups have up-to-date configuration
[!]  no changes were applied, run again with '--approve' to apply the changes

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the userdocs directory)
• Manually tested
• Added labels for change area (e.g. area/nodegroup), target version (e.g. version/0.12.0) and kind (e.g. kind/improvement)
• Make sure the title of the PR is a good description that can go into the release notes

[martina-if]

This test is actually for the upgrade part