'wdcli backup': Rework backup process

This commit reworks the backup process to dynamically find the list of
components.

internal/component/sql/backup.go

@@ -0,0 +1,35 @@
+package sql
+
+import (
+	"errors"
+	"os"
+
+	"github.com/tkw1536/goprogram/stream"
+)
+
+var errSQLBackup = errors.New("SQLBackup: Mysqldump returned non-zero exit code")
+
+func (*SQL) BackupName() string {
+	return "sql.sql"
+}
+
+// Backup makes a backup of all SQL databases into the path dest.
+func (sql *SQL) Backup(io stream.IOStream, dest string) error {
+	// open the file, TODO: Outsource this to context
+	writer, err := os.Create(dest)
+	if err != nil {
+		return err
+	}
+	defer writer.Close()
+
+	// run sqldump
+	io = io.Streams(writer, nil, nil, 0).NonInteractive()
+	code, err := sql.Stack().Exec(io, "sql", "mysqldump", "--all-databases")
+	if err != nil {
+		return err
+	}
+	if code != 0 {
+		return errSQLBackup
+	}
+	return nil
+}