[Thinkit] Add support for Open Traffic Generator in GenericTestbed, Remove PD dependencies from thinkit, Remove a potentially misleading line in the comment for ExpectLinkFlaps(), Add support for getting connected interfaces in MirrorTestbed,

[Thinkit] Add support for Open Traffic Generator in GenericTestbed, Remove PD dependencies from thinkit, Remove a potentially misleading line in the comment for ExpectLinkFlaps(), Add support for getting connected interfaces in MirrorTestbed, #2003