also catch ProcessLookupError in is_zombie_process()

Summary:
I saw an integration test failure because `eden shutdown` encountered a
`ProcessLookupError`.  This was thrown by the `proc_stat.read()` call.
Update this function to also expect this exception type if the process has
exited after we opened the file but before we could read it.

Reviewed By: strager

Differential Revision: D13521580

fbshipit-source-id: 027ad562024b5f05684e82cd940987eea2349077

eden/cli/daemon.py

@@ -88,7 +88,7 @@ def is_zombie_process(pid: int) -> bool:
             pieces = line.split()
             if len(pieces) > 2 and pieces[2] == b"Z":
                 return True
-    except FileNotFoundError:
+    except (FileNotFoundError, ProcessLookupError):
         pass
 
     return False