provide UI control for specifying ESXi VLAN interface

- when nova-network is configured to use VlanManager network manager in
  [vmware] section we can specify which hardware interface on ESXi hosts
  will be used for networking
- restrict control: it is shown only when VlanManager was selected on
  the Networks tab, otherwise it becomes invisible

DocImpact
Closes-bug: #1397293

Change-Id: I1b76b0670e7c610420f75a58cade5ac9ec2aa2d0
Merge "provide UI control for specifying ESXi VLAN interface"