Adding CLI for the migration tool (#154)

* Initial commit for the corefile-tool cli for the migration tool

* cleanup implementation

* nit

* add fn to get corefile path

* add released command and improve readme

kubernetes/corefile-tool/cmd/migrate.go

@@ -0,0 +1,56 @@
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/coredns/deployment/kubernetes/migration"
+
+	"github.com/spf13/cobra"
+)
+
+// NewMigrateCmd represents the migrate command
+func NewMigrateCmd() *cobra.Command {
+	var migrateCmd = &cobra.Command{
+		Use:   "migrate",
+		Short: "Migrate your CoreDNS corefile",
+		Example: `# Migrate CoreDNS from v1.4.0 to v1.5.0 and handle deprecations . 
+corefile-tool migrate --from 1.4.0 --to 1.5.0 --corefile /path/to/Corefile  --deprecations true
+
+# Migrate CoreDNS from v1.2.2 to v1.3.1 and do not handle deprecations .
+corefile-tool migrate --from 1.2.2 --to 1.3.1 --corefile /path/to/Corefile  --deprecations false`,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			from, _ := cmd.Flags().GetString("from")
+			to, _ := cmd.Flags().GetString("to")
+			corefile, _ := cmd.Flags().GetString("corefile")
+			deprecations, _ := cmd.Flags().GetBool("deprecations")
+
+			migrated, err := migrateCorefileFromPath(from, to, corefile, deprecations)
+			if err != nil {
+				return fmt.Errorf("error while migration: %v \n", err)
+			}
+			fmt.Println(migrated)
+			return nil
+		},
+	}
+	migrateCmd.Flags().String("from", "", "Required: The version you are migrating from. ")
+	migrateCmd.MarkFlagRequired("from")
+	migrateCmd.Flags().String("to", "", "Required: The version you are migrating to.")
+	migrateCmd.MarkFlagRequired("to")
+	migrateCmd.Flags().String("corefile", "", "Required: The path where your Corefile is located.")
+	migrateCmd.MarkFlagRequired("corefile")
+	migrateCmd.Flags().Bool("deprecations", false, "Required: Specify whether you want to handle plugin deprecations. [True | False] ")
+	migrateCmd.MarkFlagRequired("deprecations")
+
+	return migrateCmd
+}
+
+// migrateCorefileFromPath takes the path where the Corefile is located and returns the deprecated plugins or directives
+// present in the Corefile.
+func migrateCorefileFromPath(fromCoreDNSVersion, toCoreDNSVersion, corefilePath string, deprecations bool) (string, error) {
+	fileBytes, err := getCorefileFromPath(corefilePath)
+	if err != nil {
+		return "", err
+	}
+	corefileStr := string(fileBytes)
+	return migration.Migrate(fromCoreDNSVersion, toCoreDNSVersion, corefileStr, deprecations)
+}