Refactor the mechanism for creating netgraph-based pseudo

Refactor the mechanism for creating netgraph-based pseudo
interfaces (ng_iface and ng_eiface) so that:

a) we don't need a specialized version of ngctl userland utility;
b) that in FreeBSD 7.0 netgraph nodes are not renamed when
   interfaces are assigned to other vimages;

Introduce a helper array "ngnodemap" which provides name mapping
between kernel view of netgraph space, and IMUNES view of node
naming.

When creating links, do not insert a ng_pipe node between the
endpoints, given that ng_pipe is not yet ported to FreeBSD 7.0.
Instead, endpoint nodes are connected back to back, which means
that currently we will be able to construct topologies, but not
emulate link properties and impairments.

Use vimageCleanup instead of cleanupCfg, since it seems that the
later is defunct, at least on FreeBSD 7.0

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