vrf: Handle ignore interface when verifying desired state

During verification process, when post apply state does not match with
desired state due to VRF port been marked as `state: ignore`.

This is caused by `Interface::remove_port()` silently ignore VRF
interface when been invoked by `Interfaces::remove_unknown_type_port()`
during verification process.

Besides adding `VrfInterface::remove_port()`, added error log to
`Interface::remove_port()` when got unexpected interface type instead of
silently ignore.

Both unit test cases and integration test case are included.

Resolves: https://issues.redhat.com/browse/RHEL-1417

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