Memento alarms

As discussed, it looks like monit does run them in sequence.  However, almost all of our poll scripts do this (apart from the cassandra one, which runs nodetool niced so may be just as bad), so I'm reluctant to change this now.  I'll raise an issue against the general probem - I suspect we may need to daemonize the poll scripts and use some kind of file existence check to communicate status back to monit.