[QOS] Skip showing unnecessary warning message

[vivekrnv]

What I did

Don't show an unnecessary warning message (Operation not completed successfully, please save and reload configuration.) during config qos reload

To repro:

root@sonic:/home/admin# sonic-cfggen -H -k Mellanox-SN4700-O8V48 --preset t1 > /tmp/default_config.json

root@sonic:/home/admin# config qos reload
Operation not completed successfully, please save and reload configuration.

Running command: /usr/local/bin/sonic-cfggen -d -t /usr/share/sonic/device/x86_64-mlnx_msn4700-r0/Mellanox-SN4700-O8V48/buffers_dynamic.json.j2,/tmp/cfg_buffer.json -t /usr/share/sonic/device/x86_64-mlnx_msn4700-r0/Mellanox-SN4700-O8V48/qos.json.j2,/tmp/cfg_qos.json -y /etc/sonic/sonic_version.yml
Running command: /usr/local/bin/sonic-cfggen -j /tmp/cfg_buffer.json -j /tmp/cfg_qos.json --write-to-db

Buffer calculation model updated, restarting swss is required to take effect

How I did it

When in traditional buffer mode, qos reload will not wait for tables to be cleared, so it will set the timeout to 0 in the _wait_until_clear call. But today, this prints an error log and exits.

Thus fixed to not print the error log when the timeout is zero.

How to verify it

UT and manual testing

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).