Use correct param in ReadPostmasterTempFile.remote call

"remoteHost" is not a parameter to ReadPostmasterTempFile.remote(),
fix by just passing the value. The ReadPostmasterTempFile __init__
does however have a remoteHost parameter, which is likely where the
confusion occurred.

This codepath was rarely executed, but when reached it would create
the following error message:

  [ERROR]:-Failed to stop standby. Attempting forceful termination of standby process
  [CRITICAL]:-gpstop failed. (Reason='remote() got an unexpected keyword argument 'remoteHost'') exiting...
Reviewed-by: NJimmy Yih <jyih@pivotal.io>

gpMgmt/bin/gpstop

@@ -508,7 +508,7 @@ class GpStop:
                     logger.error('Failed to stop standby. Attempting forceful termination of standby process')
                     (succeeded, mypid, file_datadir) = pg.ReadPostmasterTempFile.remote("Read standby tmp file",
                                                                                         self.dburl.pgport,
-                                                                                        remoteHost=standby.hostname).getResults()
+                                                                                        standby.hostname).getResults()
                     unix.kill_9_segment_processes(self.master_datadir, self.dburl.pgport, mypid)
                     if not pg.DbStatus.remote('checking status of standby master instance', standby, standby.hostname):
                         logger.info("Successfully shutdown master standby process on %s" % standby.hostname)