Attachable containers they are tasks with no service associated
their cleanup was not done properly so it was possible to have
a leak of their name resolution if that was the last container
on the network.
Cleanupservicebindings was not able to do the cleanup because there
is no service, while also the notification of the delete arrives
after that the network is already being cleaned
Signed-off-by: Flavio Crisciani <flavio.crisciani@docker.com>