VLAN interfaces names are not sufficiently unique in some circumstances

[hinchliff]

As noted in #157, there are cases where the interfaces used to help distinguish VLAN are not sufficiently unique, and can cause manifest display issues.

[ibaldin]

Because interface names on e.g. ION connections are inherited from substrate descriptions, they end up not being unique if e.g. there are two connections coming out towards a multi-point connection from the same domain (has to be from a BM and a VM, because 2xVM connection collapses to a single connection to the multipoint).

The lack of name uniqueness prevents proper reconstruction of paths as shown in #157 by flukes, although does not affect the provisioning.