[chassis][drop counters tests] Use NO_DROPS group for DNX platforms

[smaheshm]

Description of PR

On DNX platform use "NO_DROPS" group to verify packets are dropped, and not forwarded.
At this point DNX BRCM SAI has not implemented drop counters, which is not trivial to implement due to DNX forwarding pipeline architecture.
DNX may also not be able to support drop counters for all the scenarios listed in test cases.

Summary:
Fixes # (issue)

Type of change

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

Back port request

• 201911
• 202012

Approach

What is the motivation for this PR?

Pass the drop counters test case on DNX platform

How did you do it?

Use "NO_DROPS" group to verify packets are not forwarded

How did you verify/test it?

samaddik@str-serv-acs-14:/var/sonic-mgmt/tests$ pytest -rsx drop_packets/test_drop_counters.py  --testbed=vms26-t2-7800-1 --topology="t2,any" --inventory=../ansible/str2,../ansible/veos  --testbed_file=../ansible/testbed.yaml --host-pattern=str2-7804-lc3-1  --module-path=../ansible/library  --skip_sanity
/usr/local/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py:44: CryptographyDeprecationWarning: Python 2 is no longer supported by the Python core team. Support for it is now deprecated in cryptography, and will be removed in the next release.
  from cryptography.exceptions import InvalidSignature
============================================================================================================ test session starts ============================================================================================================
platform linux2 -- Python 2.7.17, pytest-4.6.5, py-1.10.0, pluggy-0.13.1
ansible: 2.8.12
rootdir: /var/sonic-mgmt/tests, inifile: pytest.ini
plugins: forked-1.3.0, metadata-1.11.0, xdist-1.28.0, html-1.22.1, repeat-0.9.1, ansible-2.2.2
collecting ... /usr/local/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py:44: CryptographyDeprecationWarning: Python 2 is no longer supported by the Python core team. Support for it is now deprecated in cryptography, and will be removed in the next release.
  from cryptography.exceptions import InvalidSignature
collected 102 items

drop_packets/test_drop_counters.py ssssss.s..s..s..s...ss..sss....ssss....ssssss.s....sss....s...ss..ssssssssssssssssss.s.ssssss.s.sss.s.                                                                                             [100%]

============================================================================================================= warnings summary ==============================================================================================================
/usr/local/lib/python2.7/dist-packages/_pytest/config/__init__.py:538
  /usr/local/lib/python2.7/dist-packages/_pytest/config/__init__.py:538: PytestAssertRewriteWarning: Module already imported so cannot be rewritten: tests.common.dualtor
    self.import_plugin(import_spec)

-- Docs: https://docs.pytest.org/en/latest/warnings.html
========================================================================================================== short test summary info ==========================================================================================================
SKIPPED [2] /var/sonic-mgmt/tests/drop_packets/test_drop_counters.py:266: Test case requires explicit fanout support
SKIPPED [2] /var/sonic-mgmt/tests/common/helpers/assertions.py:13: BRCM does not drop SIP class E packets
SKIPPED [3] drop_packets/drop_packets.py: SONiC can't enable loop-back filter feature
SKIPPED [3] drop_packets/drop_packets.py: Not supported on Broadcom platforms
SKIPPED [2] /var/sonic-mgmt/tests/drop_packets/drop_packets.py:400: Test case requires explicit fanout support
SKIPPED [32] /var/sonic-mgmt/tests/drop_packets/drop_packets.py:229: No vlan_members available
SKIPPED [2] /var/sonic-mgmt/tests/drop_packets/drop_packets.py:439: Test case requires explicit fanout support
SKIPPED [2] /var/sonic-mgmt/tests/common/helpers/assertions.py:13: BRCM does not drop DIP link local packets
SKIPPED [12] /var/sonic-mgmt/tests/drop_packets/drop_packets.py:853: Test case requires explicit fanout support
SKIPPED [2] /var/sonic-mgmt/tests/common/helpers/assertions.py:13: BRCM does not drop SIP link local packets
=========================================================================================== 40 passed, 62 skipped, 1 warnings in 1465.17 seconds ============================================================================================
Exception AttributeError: "'NoneType' object has no attribute 'close'" in <bound method EventDescriptor.__del__ of <ptf.ptfutils.EventDescriptor instance at 0x7f1472c04c30>> ignored
samaddik@str-serv-acs-14:/var/sonic-mgmt/tests$

Any platform specific information?

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

Documentation

[smaheshm]

FYI: Added platform check for every case instead of doing it once in a common place since drop counter supported may be added in DNX platform for specific cases.

[smaheshm]

Depends on sonic-net/sonic-buildimage#8542

[rlhui]

@tjchadaga - please take up this. Thanks.