Stitcher should allow specifying VLAN

[ahelsing]

For testing purposes, sometimes you want to specify exactly what VLAN To use on a specific link/hop. You can do this now using a bunch of excludeHops arguments, but it would be nice to allow doing this more explicitly.

To really do this would require the SCS to support that interface. But stitcher could translate some command line argument into the proper set of excludeHops.

[nbastin]

FWIW you can use the geni-lib stitching interface to do this