[test_po_update] Fails due to found "mclag" errors in syslog

[yvolynets-mlnx]

Description
Test test_po_update from pc/test_po_update.py fails because during test case execution there were printed errors to the DUT syslog, and loganalyzer match this errors.

Steps to reproduce the issue:

1. Run test case on T0 topology:
   py.test $PYTEST_COMMON_OPTS pc/test_po_update.py

Describe the results you received:

LogAnalyzerError:
{'expect_messages': {'/tmp/pytest-run/syslog.2020-04-29-14:04:23': []},
 'match_files': {'/tmp/pytest-run/syslog.2020-04-29-14:04:23': {'expected_match': 0,
                                                                'match': 5}},
 'match_messages': {'/tmp/pytest-run/syslog.2020-04-29-14:04:23': ['Apr 29 14:02:16.465750 [DUT_NAME] WARNING iccpd#iccpd: message repeated 46 times: [ [iccp_connect_syncd.WARN] Failed to connect to mclag syncd: errno str Connection refused]\n',
                                                                   'Apr 29 14:02:31.865508 [DUT_NAME] WARNING iccpd#iccpd: [iccp_connect_syncd.WARN] Failed to connect to mclag syncd: errno str Connection refused\n',
                                                                   'Apr 29 14:03:23.870157 [DUT_NAME] WARNING iccpd#iccpd: [iccp_connect_syncd.WARN] Failed to connect to mclag syncd: errno str Connection refused\n',
                                                                   'Apr 29 14:03:49.920659 [DUT_NAME] WARNING iccpd#iccpd: [local_if_destroy.WARN] Destroy interface PortChannel999, 202\n',
                                                                   'Apr 29 14:04:14.558838 [DUT_NAME] WARNING iccpd#iccpd: [iccp_connect_syncd.WARN] Failed to connect to mclag syncd: errno str Connection refused\n']},
 'total': {'expected_match': 0, 'expected_missing_match': 0, 'match': 5},
 'unused_expected_regexp': []}

Describe the results you expected:
Error logs should not be printed to the syslog.

Additional information you deem important:
mclag functionality should be verified.

It is 100% reproducible on the latest SONiC master.

**Output of `show version`:**

```
(paste your output here)
```

**Attach debug file `sudo generate_dump`:**

```
(paste your output here)
```

[lguohan]

move to buildimage repo and addressed there.

[lguohan]

iccpd needs to triage the log message. check #4404 , iccpd needs to be disabled by default.

[jianjundong]

@lguohan
The reason of this error log is ICCPD can not establish TCP connection to MCLAGSYNCD. The commit ID of PR 'add mclagsyncd (#811)' is 0de72da, 'sonic-swss' may be pushed or cherry-picked to this ID.