Add several controls from NS file.  * usewatunnels - Allow users to turn off widearea tunnels.  * multiplex_factor - Allow user to specify vnode multiplex factor.  * trivial_ok - Allow user to specify collocation okay for link.
Add several controls from NS file.
 * usewatunnels - Allow users to turn off widearea tunnels.
 * multiplex_factor - Allow user to specify vnode multiplex factor.
 * trivial_ok - Allow user to specify collocation okay for link.

More work on the veth interface support and trivial link stuff.
Appears to be operational and passes the test suite.

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome