Simplify graph analyzer interface

All you need to get next nodes to schedule is call get_next_nodes()
method -- it will work correctly for tasks in any state with any
intention. This makes graph action code much simpler.

Change-Id: Idc89e98c928b3a7d8d29a4e007658e88c4326228
Make schedule a proper method of GraphAction

After recent changes there is no sense of it being a closure inside
execute() method any more.

Change-Id: Ia06ef95a0402f4566083c0ac1893ad03e320899f
Merge "Simplify graph analyzer interface"
Merge "Make schedule a proper method of GraphAction"