[Mellanox] change the implementation of is_host() to fix a stuck issue on simx platform

[keboliu]

Why I did it

Following code to judge whether a process is running inside a docker could get stuck on the simx platform

subprocess.Popen(["docker", "--version"],
                                stdout=subprocess.PIPE,
                                stderr=subprocess.STDOUT,
                                universal_newlines=True)

When it gets stuck, the config-chassisdb service can not be successfully started, thus the system can not be booted up.

root@sonic:/# service config-chassisdb status
     config-chassisdb.service - Config chassis_db
     Loaded: loaded (/lib/systemd/system/config-chassisdb.service; enabled; vendor preset: enabled)
     Active: activating (start) since Thu 2022-12-15 09:23:02 UTC; 29min ago
   Main PID: 571 (config-chassisd)
      Tasks: 14 (limit: 9501)
     Memory: 132.4M
     CGroup: /system.slice/config-chassisdb.service
                        ├─571 /bin/bash /usr/bin/config-chassisdb
			├─575 /usr/bin/python3 /usr/local/bin/sonic-cfggen -H -v DEVICE_METADATA.localhost.platform
			├─602 /bin/sh -c sudo decode-syseeprom -m
			├─603 sudo decode-syseeprom -m
			├─607 /usr/bin/python3 /usr/local/bin/decode-syseeprom -m
			├─616 /bin/sh -c docker --version 2>/dev/null
			└─617 docker --version

How I did it

Use an alternative way to implement this function and issue can be avoided:

docker_env_file = '/.dockerenv'
return os.path.exists(docker_env_file) is False

How to verify it

run regression on real hardware and simx platform.

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

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111
• 202205
• 202211

Description for the changelog

Link to config_db schema for YANG module changes

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

[mssonicbld]

Cherry-pick PR to 202211: #13642