Fix rest_for_one and one_for_all restarting a child not terminated

In rest_for_one and one_for_all supervisors one child dying can cause
multiple children to be restarted. Previously if the child that caused
the restart is started successfully but another child fails to start,
the supervisor would not terminate this child with the other
successfully restarted children as no record of the pid was kept. Thus
the supervisor would try to start this child again. This could lead to
multiples of the same child or if the child is registered cause repeated
attempts at starting this child - until the max restart threshold was
reached. Now this child is terminated immediately after another child
fails to start - before returning to the gen_server loop.