[202012][platform/barefoot] fix faild bring up pcied

[KostiantynYarovyiBf]

Why I did it

To fix faild bring up pcied

How I did it

update syntax from pyhton3 to python2

How to verify it

docker exec pmon supervisorctl status

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106

Description for the changelog

A picture of a cute animal (not mandatory but encouraged)

[ghost]

All CLA requirements met.

[vboykox]

I believe this issue could be fixed with the diff (on both master, 202106 and 202012)

diff --git a/dockers/docker-platform-monitor/docker-pmon.supervisord.conf.j2 b/dockers/docker-platform-monitor/docker-pmon.supervisord.conf.j2
index b7eca410..1bad4ab3 100644
--- a/dockers/docker-platform-monitor/docker-pmon.supervisord.conf.j2
+++ b/dockers/docker-platform-monitor/docker-pmon.supervisord.conf.j2
@@ -150,7 +150,7 @@ dependent_startup_wait_for=rsyslogd:running
 
 {% if not skip_pcied %}
 [program:pcied]
-command=/usr/local/bin/pcied
+command={% if API_VERSION == 3 and 'pcied' not in python2_daemons %}python3 {% else %} python2 {% endif %}/usr/local/bin/pcied
 priority=10
 autostart=false
 autorestart=unexpected

Need to try.

The reason it works on master is that we have dropped python2 support there. so load_platform_pcieutil in pcied script just fallbacks to sonic_platform_base.sonic_platform.pcie version with ImportError on import sonic_plaform stage (not sonic_platform.platform)
Also if we will add own sonic_platform.pcie - it will crash on master. (Since load_platform_pcieutil will attempt to instaniate sonic_platform.platform module with python2)

After doing this we can check if we need supporting py2 in 202012.

[KostiantynYarovyiBf]

close this PR by comment @vboykox and add fix for docker-pmon.supervisord.conf.j2 in this PR:
#8543