**- Why I did it**
python2 is end of life and SONiC is going to support python3. This PR is going to support:
1. Build pmon daemons with python3
2. Install and run python3 version pmon daemons
**- How I did it**
1. Change pmon daemons make files to build bothe python2 and python3 whl
2. Change docker-platform-monitor make files to install both python2 and python3 whl
3. Change pmon docker startup files to start pmon daemons according to the supported platform API version
HLD: Azure/SONiC#646
Introducing chassisd process to monitor status of the control, line and fabric cards in a modular chassis.
- Why I did it
Modular Chassis has control-cards, line-cards and fabric-cards along with other peripherals. Chassisd will be a central entity that has visibility of the entire chassis.
- How I did it
Chassisd process will monitor cards in the main thread. Another configuation_handling_task is created to listen to CONFIG_DB for admin_status up/down events. The monitored status is persisted in REDIS-DB.
**- Why I did it**
We were building a custom version of Supervisor because I had added patches to prevent hangs and crashes if the system clock ever rolled backward. Those changes were merged into the upstream Supervisor repo as of version 3.4.0 (http://supervisord.org/changes.html#id9), therefore, we should be able to simply install the vanilla package via pip. This will also allow us to easily move to Python 3, as Python 3 support was added in version 4.0.0.
**- How I did it**
- Remove Makefiles and patches for building supervisor package from source
- Install Python 3 supervisor package version 4.2.1 in Buster base container
- Also install Python 3 version of supervisord-dependent-startup in Buster base container
- Debian package installed binary in `/usr/bin/`, but pip package installs in `/usr/local/bin/`, so rather than update all absolute paths, I changed all references to simply call `supervisord` and let the system PATH find the executable to prevent future need for changes just in case we ever need to switch back to build a Debian package, then we won't need to modify these again.
- Install Python 2 supervisor package >= 3.4.0 in Stretch and Jessie base containers
Copy proper fancontrol config file to the proper destination. Also some minor refactoring for code reuse to help prevent issues like this in the future.
Fixes a bug introduced by #4599
