tmf: Move some logic outside of HistoryBuilder

tmf: Move some logic outside of HistoryBuilder

Move the input.assignTargetSS() call outside of HistoryBuilder's
constructor. This will allow more flexibility for input/backend
types that need to instantiate their objects in a different
order than the typical "kernel input -> ss -> history tree"
trinity does (for example, partial histories).

Change-Id: I2d07b44e39e55475bd6bdfde8641d2985b7c145f
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/10280
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
IP-Clean: Patrick Tasse <patrick.tasse@gmail.com>
Tested-by: Hudson CI