Bug #1415: Fix VLAN option in Vnet templates
Currently VLAN was not set unless VLAN_ID was specified.
This commit fixes it. It also shows the option for ebtables and hides VLAN_ID option for non-administrator users.
(cherry picked from commit a74eea22fdf86c2bfc3d0b035e45522c63297626)
(cherry picked from commit 98048f42f74fb80ed623cccf94199ec001dcb600)