CLOUDSTACK-5849: Failed shutdown of the network causes network state to
be changed to 'Implemented'

Wrong network state transition

s_fsm.addTransition(State.Shutdown, Event.OperationFailed,State.Implemented

fix keeps state as Shutdown
CLOUDSTACK-5861: networks that failed to implement can not be destroyed

introduces a force option in delete network to forcifully delete a
network. This comes handy in rare cases where network fails to implenet
and network is in shutdown state, but network shutdown to rollback
implement process fails as well.