vlab: allow adding and removing switch interfaces

Signed-off-by: Daniel Baluta <daniel.baluta@gmail.com>
vlab: save links for future use

Signed-off-by: Daniel Baluta <daniel.baluta@gmail.com>
vlab: add links to switches

Signed-off-by: Daniel Baluta <daniel.baluta@gmail.com>
vlab: use the correct name for interfaces

Interface names use tap.hostname convention.

Signed-off-by: Daniel Baluta <daniel.baluta@gmail.com>