KernelAnalysis: Use Threads CoreAttributes to store "Status"

KernelAnalysis: Use Threads CoreAttributes to store "Status"

Threads core attributes were not used to store interval data, this
leads to useless NullStateValue intervals ranging from tree start
to end. This patch uses the Threads CoreNodes to store the "Status"
fields thus reducing the number of attributes and intervals.

Change-Id: Ia24b8d5226b66738a8c14d3d652879169437b95a
Signed-off-by: Loïc Prieur-Drevon <loic.prieurdrevon@gmail.com>
Reviewed-on: https://git.eclipse.org/r/70769
Reviewed-by: Hudson CI
Reviewed-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Tested-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Alexandre Montplaisir <alexmonthy@efficios.com>