Fixes#1374
When monkey starts, it launches a thread for executing post breach
actions. It then executes its propagation loop on the main thread. If
the maximum propagation depth has been reached, a
PlannedShutdownException is raised on the main thread. This results in
InfectionMonkey.cleanup() being called, which then calls
InfectionMonkey.self_delete(). self_delete() deletes the monkey binary,
but the post breach actions thread hasn't been stopped, resulting in
a trace when the thread attempts an import.
We don't need to shutdown if the maximum propagation depth is reached.
We only need to skip the propagation phase so that monkey does not
propagate further. PBAs and payloads can still be allowed to run.
Mike Salvatore
Shreya
Swimm