[test_configurable_drop_counters]Ignore loganalyzer exceptions

[yejianquan]

Description of PR

Fix loganalyzer exception of test_configurable_drop_counters.
Summary:
Fixes # (issue)

Type of change

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

Back port request

• 201911
• 202012

Approach

What is the motivation for this PR?

Fix loganalyzer exception of test_configurable_drop_counters.

How did you do it?

For the error log 1-3:
I checked the trigger of the logs, likely it's because of the double delete([sonic-clear fdb all and arp], swssconfig ) of the cleanup commands.
The second delete command(swssconfig) is used to remove the static mac record in fdb, I can see a certain record is deleted even though it's saying can't delete a non-exist record.
It may be related to the async executing of swssconfig and sonic-clear(https://github.com/sonic-net/SONiC/wiki/SONiC-Clear-FDB-CLI-Design), if I execute 'show arp' and 'show mac' between the two cleanups, the exception will not be raised.
Since a double delete has no bad effect on DUT, we can safely ignore it.

For the error log 4-5:
It should be related to debug things, we can safely ignore it too.

So we can ignore the 5 error logs.

How did you verify/test it?

Run on physical testbeds
drop_packets/test_configurable_drop_counters.py::test_neighbor_link_down[PORT_INGRESS_DROPS-L3_EGRESS_LINK_DOWN] PASSED [ 16%]
drop_packets/test_configurable_drop_counters.py::test_neighbor_link_down[SWITCH_INGRESS_DROPS-L3_EGRESS_LINK_DOWN] SKIPPED [ 33%]
drop_packets/test_configurable_drop_counters.py::test_dip_link_local[PORT_INGRESS_DROPS-DIP_LINK_LOCAL] PASSED [ 50%]
drop_packets/test_configurable_drop_counters.py::test_dip_link_local[SWITCH_INGRESS_DROPS-DIP_LINK_LOCAL] SKIPPED [ 66%]
drop_packets/test_configurable_drop_counters.py::test_sip_link_local[PORT_INGRESS_DROPS-SIP_LINK_LOCAL] PASSED [ 83%]
drop_packets/test_configurable_drop_counters.py::test_sip_link_local[SWITCH_INGRESS_DROPS-SIP_LINK_LOCAL] SKIPPED [100%]

[ZhaohuiS]

@yejianquan Not sure if this PR #5821 can solve loganalyzer issue, but I plan to hold it to check if fix of sonic-net/sonic-buildimage#11046 works.

[yejianquan]

@yejianquan Not sure if this PR #5821 can solve loganalyzer issue, but I plan to hold it to check if fix of Azure/sonic-buildimage#11046 works.

@ZhaohuiS OK, I'm pretty sure the error log 1-3 is related to your fix.
For 4-5, can @theasianpianist take a look?