[test_vlan] Fix test_vlan

[bingwang-ms]

Description of PR

Summary:
Fixes # (issue)
This PR fix two issues in test_vlan.py

1. Add a new method to capture and check packets from involved interfaces, including portchannel. If packet is captured from any port of the portchannel, the check passes.
2. VLAN priority is ignored when matching expected packets, because the VLAN priority is determined by the port and VLAN configuration.

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• Test case(new/improvement)

Approach

What is the motivation for this PR?

This PR is to fix test_vlan case.

How did you do it?

Two updates:

1. Add a new method to capture and check packets from interfaces (including portchannel);
2. VLAN priority is ignored when matching expected packets.

How did you verify/test it?

Verify it on Arista-7260cx3 DUT.

========================================================================================= test session starts =========================================================================================
platform linux2 -- Python 2.7.12, pytest-4.6.5, py-1.8.1, pluggy-0.13.1 -- /usr/bin/python
cachedir: .pytest_cache
ansible: 2.8.7
rootdir: /data/Networking-acs-sonic-mgmt/tests, inifile: pytest.ini
plugins: forked-1.1.3, xdist-1.28.0, ansible-2.2.2, repeat-0.8.0
collected 3 items                                                                                                                                                                                     

vlan/test_vlan.py::test_vlan_tc1_send_untagged PASSED                                                                                                                                           [ 33%]
vlan/test_vlan.py::test_vlan_tc2_send_tagged PASSED                                                                                                                                             [ 66%]
vlan/test_vlan.py::test_vlan_tc3_send_invalid_vid PASSED                                                                                                                                        [100%]

------------------------------------------------------------------ generated xml file: /data/Networking-acs-sonic-mgmt/tests/tr.xml -------------------------------------------------------------------
===================================================================================== 3 passed in 416.55 seconds =====================================================================================

Any platform specific information?

No.

Supported testbed topology if it's a new test case?

N/A

Documentation

No.

[lgtm-com]

This pull request introduces 1 alert when merging cd3f5b8 into d31cc1d - view on LGTM.com

new alerts:

• 1 for Unused import

[prsunny]

lgtm