Hob: avoid the empty white space appearing on top of the gtk.ComboBox

Avoid the empty white space appearing on top of the machine selection combo
box and the image selection combo box in the "Image configuration" screen

[Yocto #2166]

(Bitbake rev: 9d30ad56803c67d2dc7ebddd7c339038438f02ba)

Signed-off-by: Shane Wang <shane.wang@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/ui/crumbs/imageconfigurationpage.py

@@ -143,6 +143,7 @@ class ImageConfigurationPage (HobPage):
         self.machine_title_desc.set_markup(mark)
 
         self.machine_combo = gtk.combo_box_new_text()
+        self.machine_combo.set_wrap_width(1)
         self.machine_combo.connect("changed", self.machine_combo_changed_cb)
 
         icon_file = hic.ICON_LAYERS_DISPLAY_FILE
@@ -191,6 +192,7 @@ class ImageConfigurationPage (HobPage):
         self.image_title_desc.set_markup(mark)
 
         self.image_combo = gtk.combo_box_new_text()
+        self.image_combo.set_wrap_width(1)
         self.image_combo_id = self.image_combo.connect("changed", self.image_combo_changed_cb)
 
         self.image_desc = gtk.Label()