Analysis: Add the active path module

Analysis: Add the active path module

This module computes the active path from a execution graph. The active
path of a given task has all the blockings replaced recursively by the
edges representing the cause of the wait at the system level.

Change-Id: Ie19b461ebe5ad595bca43b55f380ce28db416445
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Signed-off-by: Francis Giraldeau <francis.giraldeau@gmail.com>
Reviewed-on: https://git.eclipse.org/r/51081
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>