def _lookup_vhd_path(self, instance_name, vhd_path_func):
    vhd_path = None
    for format_ext in ['vhd', 'vhdx']:
        test_path = vhd_path_func(instance_name, format_ext)
        if self.exists(test_path):
            vhd_path = test_path
            break
    return vhd_path
def _lookup_vhd_path(self, instance_name, vhd_path_func):
    vhd_path = None
    for format_ext in ['vhd', 'vhdx']:
        test_path = vhd_path_func(instance_name, format_ext)
        if self.exists(test_path):
            vhd_path = test_path
            break
    return vhd_path