[202205][Mellanox] change the implementation of is_host() to fix a stuck issue on simx platform (#13101)

This PR is to backport #13100 to the 202205 branch since can not be cleanly cherry-picked.

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.

platform/mellanox/mlnx-platform-api/sonic_platform/utils.py

@@ -186,18 +186,8 @@ def is_host():
     Test whether current process is running on the host or an docker
     return True for host and False for docker
     """
-    try:
-        proc = subprocess.Popen("docker --version 2>/dev/null",
-                                stdout=subprocess.PIPE,
-                                shell=True,
-                                stderr=subprocess.STDOUT,
-                                universal_newlines=True)
-        stdout = proc.communicate()[0]
-        proc.wait()
-        result = stdout.rstrip('\n')
-        return result != ''
-    except OSError as e:
-        return False
+    docker_env_file = '/.dockerenv'
+    return os.path.exists(docker_env_file) is False
 
 
 def default_return(return_value, log_func=logger.log_debug):