With this change a link between two subflows caused by task dependency
does not impose execution ordering between all tasks of that subflows
any more: only provider and consumer of the dependency are now linked.
For some cases this is a major optimization, as it allows more
independent parts of the flow to be executed or reverted in parallel. It
also allows, for example, converting parts of flow into subflows without
loosing performance.
Because with this change parts of parent flow that depend on some tasks
in subflow can be executed before all tasks in the subflow are
completed, graph analyzer is changed to not stop at subflow border when
iterating subgraphs.
Change-Id: I45587a4e851febe3c43cfa7b74bdfc50f61e0279
4559fdd841