Add set_spawn_error_hook to TaskManager

This patch is adding a way to create a hook on the TaskManager that gets
called upon an exception being raised. The task.spawn_after() do not
raise any exception making it impossible to add some logic around it in
case something goes bad with the method being executed by the greenthread.

Partial-Bug: #1331494
Change-Id: I5755df359a6e8678b64d4d59c25a9192f575b13d
Merge "Add set_spawn_error_hook to TaskManager"