Migrate "disk space" monitor to Prometheus
Migrate "disk space" monitor to Prometheus

Original DataDog alert:
max(last_5m):max:system.disk.in_use{deploy_env:prod,!device:/dev/loop0,!device:tmpfs,!device:cgroup,!device:udev,!device:/var/vcap/data/root_log,!device:/var/vcap/data/root_tmp} by {bosh-job,device,bosh-index} * 100 > 85

In prometheus we don't have the disk usage per device, it's categorised as
system/persistent/ephemeral. In our case I think these metrics should be
enough.

Also the firehose-exporter exposes the inode usages too, which we should also
alert on.

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf