Make the initialize of EditRemoteLogin more smooth.

Hi folks,
This patch try to make the initialize of EditRemoteLogin more smooth. 
(Or maybe it should be fixed it in deepin-ui?)
I think using place_center() after show_all() is not a good way to move the dialog to the center of it's parent window. Because it will generate a 'moving shadow', it not a perfect way. ;)

Thanks for any review.