cherry pick f41a534 (pytorch#2889)

torch_xla/__init__.py

@@ -13,9 +13,11 @@
 
 
 def server_is_alive():
-  return len(
-      subprocess.Popen(['pgrep', '-f', XRT_SERVER_REGEX],
-                       stdout=subprocess.PIPE).stdout.readline()) != 0
+  # pgrep returns 0 when at least one running process matches the requested name.
+  # Otherwise, the exit code is 1. If pgrep is not availiable in the system, it
+  # will return an exit code 127.
+  return subprocess.getstatusoutput(
+      'pgrep -f "{}"'.format(XRT_SERVER_REGEX))[0] == 0
 
 
 def _maybe_select_tpu_version():