ScmpEchoDemo fails with some "minimal" destinations

[tzaeschke]

When running the ScmpEchoDemo with the minimal topology, the default AS 211 can be reached, but AS 111 times out and AS 1111 causes an Exception.

Initial analysis

• AS 111 appears to be broken because 111 is an on-path AS. The current path creation algorithm does not recognize that and create an UP+DOWN path. This appears to irritate the BR in 111 and the packet is dropped. This should be resolved with the implementation of on-path path creation.
• AS 1111 appears to be broken because the echo process listens on 0.0.0.0. This somehow confuses the border router and the packet cannot be returned (port unreachable). Temporary resolution: provide a better error message (implemented in SCMP echo problems, see #96 #97). Long term solution: fix problem, e.g. by binding to a proper IP address. Side note: 0.0.0.0 is not an IPv4 address but an IPv6 mapped address (check netstat). Also: it seems this problem is limited to topologies running locally on the machine, echo in the production network is not affected.

[tzaeschke]

Shortcut + on-path was fixed in #104

[tzaeschke]

Part one is fixed. Path 2 is unclear. Won't fix, works in production, fails only in local minimal setup.