webadmin: Combobox is not align

Combobox control contains small a gap and not align to the center.

Change-Id: I632e4e15bd4a2c49e27a01635d48c4843c91cd17
Bug-Url: https://bugzilla.redhat.com/1141524
Signed-off-by: Shahar Havivi <shaharh@redhat.com>