ui: combobox label wrong alignment

The combobox label is too short which make the text overlay over the
selection in editable mode.

Change-Id: Iefafe0240d15fe9e2a0e741e4804b2b6c1a40e87
Bug-Url: https://bugzilla.redhat.com/1139201
Signed-off-by: Shahar Havivi <shaharh@redhat.com>