refactor: cluster create command

User facing changes:
* Add two sub-commands: "cluster create qemu" and "cluster create docker"
  The commands only have flags relevant to the applicable providers
* Error if invalid provider's flags are passed
* Add (QEMU only) or (docker only) at the start of the flag description
* Group flags by providers and then sort alphabetically.

Internal:
* Split common cluster creation logic into a ClusterMaker abstraction
* Split creation logic of cluster and qemu clusters
* Add basic unit tests for all the options

unrelated
* Use default kubeconfig instead of kubeconfig.SinglePath()
* If KVM is not available, log a warning and proceed without it

Signed-off-by: Orzelius <33936483+Orzelius@users.noreply.github.com>

Author: Orzelius

cmd/talosctl/cmd/mgmt/cluster/cluster.go

@@ -6,45 +6,51 @@
 package cluster
 
 import (
-	"errors"
 	"path/filepath"
 
 	"github.com/spf13/cobra"
 
 	clientconfig "github.com/siderolabs/talos/pkg/machinery/client/config"
+	"github.com/siderolabs/talos/pkg/provision/providers"
+)
+
+const (
+	// ProvisionerFlag is the flag with which the provisioner is configured.
+	ProvisionerFlag = "provisioner"
 )
 
 // Cmd represents the cluster command.
 var Cmd = &cobra.Command{
 	Use:   "cluster",
 	Short: "A collection of commands for managing local docker-based or QEMU-based clusters",
 	Long:  ``,
-	PersistentPreRunE: func(*cobra.Command, []string) error {
-		if provisionerName == docker && !bootloaderEnabled {
-			return errors.New("docker provisioner requires bootloader to be enabled")
-		}
+}
 
-		return nil
-	},
+// CmdOps are the options for the cluster command.
+type CmdOps struct {
+	ProvisionerName string
+	StateDir        string
+	ClusterName     string
 }
 
 var (
-	provisionerName string
-	stateDir        string
-	clusterName     string
-
 	defaultStateDir string
-	defaultCNIDir   string
+
+	// DefaultCNIDir is the default location of the cni binaries.
+	DefaultCNIDir string
 )
 
+// Flags are the flags of the cluster command.
+var Flags CmdOps
+
 func init() {
 	talosDir, err := clientconfig.GetTalosDirectory()
 	if err == nil {
 		defaultStateDir = filepath.Join(talosDir, "clusters")
-		defaultCNIDir = filepath.Join(talosDir, "cni")
+		DefaultCNIDir = filepath.Join(talosDir, "cni")
 	}
 
-	Cmd.PersistentFlags().StringVar(&provisionerName, "provisioner", docker, "Talos cluster provisioner to use")
-	Cmd.PersistentFlags().StringVar(&stateDir, "state", defaultStateDir, "directory path to store cluster state")
-	Cmd.PersistentFlags().StringVar(&clusterName, "name", "talos-default", "the name of the cluster")
+	Cmd.PersistentFlags().StringVar(&Flags.ProvisionerName, ProvisionerFlag, providers.DockerProviderName, "Talos cluster provisioner to use")
+	Cmd.PersistentFlags().StringVar(&Flags.StateDir, "state", defaultStateDir, "directory path to store cluster state")
+	Cmd.PersistentFlags().StringVar(&Flags.ClusterName, "name", "talos-default", "the name of the cluster")
 }