Add openshift-install ignition convert

The transition to Ignition Spec 3 with 4.6 creates a
discontinuity.  Some users want to update their bootimages,
e.g. for a cluster originally provisioned as 4.4 but upgraded
in place to 4.6, it should be possible to directly use RHCOS 4.6
bootimages for new workers.

In some cases in fact, this could be *required* for things like
adding a node with newer hardware.

The main stumbling block here is the pointer ignition config.
Since `openshift-install` already includes Ignition bits, let's
add translation capability here using
https://github.com/coreos/ign-converter
the same as the MCO uses.

xref openshift/enhancements#492 (comment)
xref https://bugzilla.redhat.com/show_bug.cgi?id=1884750

cmd/openshift-install/ignition.go

@@ -0,0 +1,74 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"os"
+
+	"github.com/pkg/errors"
+	"github.com/spf13/cobra"
+	ignv2 "github.com/coreos/ignition/config/v2_4"
+	"github.com/coreos/ign-converter/translate/v24tov31"
+)
+
+func newIgnitionCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "ignition",
+		Short: "Operations on Ignition configs",
+		Long: `Operations on Ignition configs
+
+See sub-operations for details.`,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return cmd.Help()
+		},
+	}
+	cmd.AddCommand(newIgnitionConvertCmd())
+	return cmd
+}
+
+var (
+	ignitionConvertOpts struct {
+		source string
+		dest   string
+	}
+)
+
+func newIgnitionConvertCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "convert",
+		Short: "Convert a Spec2 config to Spec 3",
+		Long: `Convert a Spec2 config to Spec 3
+
+OpenShift versions 4.6 and above use Ignition Spec 3.  This
+command can be used to translate the "pointer config" generated
+by a prior version of openshift-install to Spec 3, so that
+it can be used with newer bootimages.
+`,
+		Args: cobra.ExactArgs(2),
+
+		RunE: func(cmd *cobra.Command, args []string) error {
+			dataIn, err := ioutil.ReadFile(args[0])
+			if err != nil {
+				return errors.Wrapf(err, "failed to read %s", args[0])
+			}
+			dest := args[1]
+			cfg, rpt, err := ignv2.Parse(dataIn)
+			fmt.Fprintf(os.Stderr, "%s", rpt.String())
+			if err != nil || rpt.IsFatal() {
+				return errors.Errorf("Error parsing spec v2 config: %v\n%v", err, rpt)
+			}
+
+			newCfg, err := v24tov31.Translate(cfg, nil)
+			if err != nil {
+				return errors.Wrapf(err, "translation failed", err)
+			}
+			dataOut, err := json.Marshal(newCfg)
+			if err != nil {
+				return errors.Wrapf(err, "failed to marshal JSON")
+			}
+			return ioutil.WriteFile(dest, dataOut, 0666)
+		},
+	}
+	return cmd
+}

cmd/openshift-install/main.go

@@ -63,6 +63,7 @@ func installerMain() {
 		newCompletionCmd(),
 		newMigrateCmd(),
 		newExplainCmd(),
+		newIgnitionCmd(),
 	} {
 		rootCmd.AddCommand(subCmd)
 	}

go.mod

@@ -20,6 +20,8 @@ require (
 	github.com/c4milo/gotoolkit v0.0.0-20190525173301-67483a18c17a // indirect
 	github.com/clarketm/json v1.14.1
 	github.com/containers/image v3.0.2+incompatible
+	github.com/coreos/ign-converter v0.0.0-20200918193805-44d462f1c700
+	github.com/coreos/ignition v0.35.0
 	github.com/coreos/ignition/v2 v2.3.0
 	github.com/dmacvicar/terraform-provider-libvirt v0.6.2
 	github.com/frankban/quicktest v1.7.2 // indirect

go.sum

@@ -374,6 +374,8 @@ github.com/coreos/go-systemd v0.0.0-20190719114852-fd7a80b32e1f/go.mod h1:F5haX7
 github.com/coreos/go-systemd/v22 v22.0.0 h1:XJIw/+VlJ+87J+doOxznsAWIdmWuViOVhkQamW5YV28=
 github.com/coreos/go-systemd/v22 v22.0.0/go.mod h1:xO0FLkIi5MaZafQlIrOotqXZ90ih+1atmu1JpKERPPk=
 github.com/coreos/ign-converter v0.0.0-20200629171308-e40a44f244c5/go.mod h1:LNu0WTt8iVH/WJH15R/SjZw7AdyY2qAyf9ILZTCBvho=
+github.com/coreos/ign-converter v0.0.0-20200918193805-44d462f1c700 h1:Un1+sTzUeZGSr0gFIpHMUEZnwfBJeswD1ZJS05W8m/Y=
+github.com/coreos/ign-converter v0.0.0-20200918193805-44d462f1c700/go.mod h1:LNu0WTt8iVH/WJH15R/SjZw7AdyY2qAyf9ILZTCBvho=
 github.com/coreos/ignition v0.33.0/go.mod h1:WJQapxzEn9DE0ryxsGvm8QnBajm/XsS/PkrDqSpz+bA=
 github.com/coreos/ignition v0.34.0/go.mod h1:WJQapxzEn9DE0ryxsGvm8QnBajm/XsS/PkrDqSpz+bA=
 github.com/coreos/ignition v0.35.0 h1:UFodoYq1mOPrbEjtxIsZbThcDyQwAI1owczRDqWmKkQ=