Consider change task siblings & their descendants for duplicates

Previously tasks were only considered to potentially be duplicates if
they were in a direct ancestry line of each other. Expand the
possibility of a match to include any descendants of the same base
tasksFactory.

Release-Notes: More changes may be marked task duplicates
Change-Id: Iad33af6c6a7db2d242a0c30b9344573c71f58bcd