This moves to a more generic config parser that doesn't have plugins
parsing part of the tree.
I understand why it ended up that way; we have "partitions" key which
has special semantics compared to others keys and there was a desire
to keep it isolated from core tree->graph code. But this isn't really
isolated; you have to reverse-engineer several module-crossing
boundaries, extras classes and repetitive recursive functions.
Ultimately, plugins should have access to the node graph, but not
participate in configuration parsing. This way we ensure that plugins
can't invent new methods of configuration parsing.
Note: unit tests produce the same tree -> graph conversion as the old
method. i.e. this is not intended to have a functional change.
Change-Id: I8a5d62a076a5a50597f2f1df3a8615afba6dadb2
00da1982ce