fix initial attempt to incorporate LAUNCHING state and corresponding transition
remove flag LAUNCH_CHILDREN_ON_START (which was used to facilitate testing of
  the launch of the children in on_start and also in INITIALIZE). The launch of the children is now always started (via a greenlet) in on_start.
Merge pull request #1010 from carueda/platform_agent_R2C4

fix initial attempt to incorporate LAUNCHING state and corresponding transition, and add needed associated handling