Use 'set -e' in bootstrap helpers.

The salt bootstrapping helpers would touch their 'flag file' regardless
of the actual success/failure of their subcommands. This masked some
pretty ugly failures, as salt would subsequently skip them in later
runs.
Explicitly manage /srv/graphite/storage perms

This has stemmed out of the Vagrant setup i'm doing for the
monitoring system -- previously /srv/graphite/storage would be
automatically created with the right perms. Now we need to account
for it possibly being there before we start - with incorrect ownership.
Merge pull request #20 from ministryofjustice/error_handling_db_seed

Use 'set -e' in bootstrap helpers.
Merge pull request #21 from ministryofjustice/manage_storage_dir

Explicitly manage /srv/graphite/storage perms
Ask statsd plugin go count number of timed events

Other hidden options are:

* TimerUpper
* TimerLower
* TimerCount
* TimerSum

(From <https://github.com/collectd/collectd/blob/collectd-5.4.0/src/statsd.c#L613>)
Add other statsd timers, and associated carbon aggregation policies