Fix 'NoSuchProcess' exception in process_checker (sonic-net#5716)

The psutil library used in process_checker create a cache for each
process when calling process_iter. So, there is some possibility that
one process exists when calling process_iter, but not exists when
calling cmdline, which will raise a NoSuchProcess exception. This commit
fix the issue.

Signed-off-by: bingwang <bingwang@microsoft.com>

files/image_config/monit/process_checker

@@ -28,9 +28,12 @@ def check_process_existence(container_name, process_cmdline):
             # state, then it will be marked as 'running'.
             is_running = False
             for process in psutil.process_iter(["cmdline", "status"]):
-                if ((' '.join(process.cmdline())).startswith(process_cmdline) and process.status() in ["running", "sleeping"]):
-                    is_running = True
-                    break
+                try:
+                    if ((' '.join(process.cmdline())).startswith(process_cmdline) and process.status() in ["running", "sleeping"]):
+                        is_running = True
+                        break
+                except psutil.NoSuchProcess:
+                    pass
 
             if not is_running:
                 # If this script is run by Monit, then the following output will be appended to