Update gpstop

When the environment variables COORDINATOR_DATA_DIRECTORY are not set correctly, the error message is meaningless

Author: water32

gpMgmt/bin/gpstop

@@ -7,6 +7,7 @@
 #
 # import mainUtils FIRST to get python version check
 from gppylib.mainUtils import *
+from gppylib.commands.gp import *
 
 import os, sys
 import signal
@@ -959,9 +960,7 @@ class GpStop:
 
         if is_external_fts:
             if options.fts_hosts is None:
-                coordinator_data_directory = os.getenv('COORDINATOR_DATA_DIRECTORY')
-                if coordinator_data_directory is None:
-                    coordinator_data_directory = options.coordinatorDataDirectory
+                coordinator_data_directory = get_coordinatordatadir()
 
                 options.fts_hosts = coordinator_data_directory + '/config' + '/fts_host'