test: Fix `test_attach_new_vlan_of_new_bond_to_exist_bridge`

The `test_attach_new_vlan_of_new_bond_to_exist_bridge` incorrectly
set the VLAN to `eth1` as parent which is not the purpose of testing,
it should be use newly created bond99 as parent.

Signed-off-by: Gris Ge <fge@redhat.com>