By using childs weights for scheduling we can unlock
concurrent and decrease total time of execution.
As an example consider next variant:
Tasks A and B can't run concurrently because of node-limit.
Tasks A and C have logical dependency, and thus not concurrent.
Tasks B and C will be executed on different nodes, and doesnt
have any logical dependency.
As A and B doesnt have parents we may schedule any of this task
and logically execution will be correct, but in case if we will choose
B total time of execution will be - B + A + C, BUT
if we will select A - total time of execution may be reduced,
and will take in total - A + max(B, C).
Change-Id: I52a6c20e8c3d729ed20da822f45cbad90e51f2df
Closes-Bug: 1554105
e2cfa869d8