Get the user accounts specified in metadata server contents.

    Args:
      metadata_dict: json, the deserialized contents of the metadata server.

    Returns:
      dict, a mapping of the form: {'username': ['sshkey1, 'sshkey2', ...]}.

def _GetAccountsData(self, metadata_dict):
    """Get the user accounts specified in metadata server contents.

    Args:
      metadata_dict: json, the deserialized contents of the metadata server.

    Returns:
      dict, a mapping of the form: {'username': ['sshkey1, 'sshkey2', ...]}.
    """
    instance_data, project_data = self._GetInstanceAndProjectAttributes(
        metadata_dict)
    valid_keys = [instance_data.get('sshKeys'), instance_data.get('ssh-keys')]
    block_project = instance_data.get('block-project-ssh-keys', '').lower()
    if block_project != 'true' and not instance_data.get('sshKeys'):
      valid_keys.append(project_data.get('ssh-keys'))
      valid_keys.append(project_data.get('sshKeys'))
    accounts_data = '\n'.join([key for key in valid_keys if key])
    return self._ParseAccountsData(accounts_data)