Get a parent and the children using the parent name
You can either adjust your join condition
SELECT child.id
  FROM servers AS parent 
  LEFT JOIN servers AS child
    ON (child.parent_id = parent.id
     OR child.id = parent.id)
  WHERE parent.name = 'kvm01';

or use UNION / UNION ALL to retrieve the parent record separately:
SELECT child.id
  FROM servers AS parent 
  LEFT JOIN servers AS child
    ON child.parent_id = parent.id
  WHERE parent.name = 'kvm01'
UNION ALL
SELECT parent.id
  FROM servers AS parent
  WHERE parent.name = 'kvm01';