Backport https://github.com/Azure/sonic-buildimage/pull/9068 to 202012
#### Why I did it
Command `monit summary -B` can no longer display the status for each critical process, system-health should not depend on it and need find a way to monitor the status of critical processes. The PR is to address that. monit is still used by system-health to do file system check as well as customize check.
#### How I did it
1. Get container names from FEATURE table
2. For each container, collect critical process names from file critical_processes
3. Use “docker exec -it <container_name> bash -c ‘supervisorctl status’” to get processes status inside container, parse the output and check if any critical processes exit
#### How to verify it
1. Add unit test case to cover it
2. Adjust sonic-mgmt cases to cover it
3. Manual test
* system health first commit
* system health daemon first commit
* Finish healthd
* Changes due to lower layer logic change
* Get ASIC temperature from TEMPERATURE_INFO table
* Add system health make rule and service files
* fix bugs found during manual test
* Change make file to install system-health library to host
* Set system LED to blink on bootup time
* Caught exceptions in system health checker to make it more robust
* fix issue that fan/psu presence will always be true
* fix issue for external checker
* move system-health service to right after rc-local service
* Set system-health service start after database service
* Get system up time via /proc/uptime
* Provide more information in stat for CLI to use
* fix typo
* Set default category to External for external checker
* If external checker reported OK, save it to stat too
* Trim string for external checker output
* fix issue: PSU voltage check always return OK
* Add unit test cases for system health library
* Fix LGTM warnings
* fix demo comments: 1. get boot up timeout from monit configuration file; 2. set system led in library instead of daemon
* Remove boot_timeout configuration because it will get from monit config file
* Fix argument miss
* fix unit test failure
* fix issue: summary status is not correct
* Fix format issues found in code review
* rename th to threshold to make it clearer
* Fix review comment: 1. add a .dep file for system health; 2. deprecated daemon_base and uses sonic-py-common instead
* Fix unit test failure
* Fix LGTM alert
* Fix LGTM alert
* Fix review comments
* Fix review comment
* 1. Add relevant comments for system health; 2. rename external_checker to user_define_checker
* Ignore check for unknown service type
* Fix unit test issue
* Rename user define checker to user defined checker
* Rename user_define_checkers to user_defined_checkers for configuration file
* Renmae file user_define_checker.py -> user_defined_checker.py
* Fix typo
* Adjust import order for config.py
Co-authored-by: Joe LeVeque <jleveque@users.noreply.github.com>
* Adjust import order for src/system-health/health_checker/hardware_checker.py
Co-authored-by: Joe LeVeque <jleveque@users.noreply.github.com>
* Adjust import order for src/system-health/scripts/healthd
Co-authored-by: Joe LeVeque <jleveque@users.noreply.github.com>
* Adjust import orders in src/system-health/tests/test_system_health.py
* Fix typo
* Add new line after import
* If system health configuration file not exist, healthd should exit
* Fix indent and enable pytest coverage
* Fix typo
* Fix typo
* Remove global logger and use log functions inherited from super class
* Change info level logger to notice level
Co-authored-by: Joe LeVeque <jleveque@users.noreply.github.com>
