Create Prometheus metric exposing the EFS id
Create Prometheus metric exposing the EFS id

```nubis_efs{efs_id="$EFS_ID",efs_name="$EFS_NAME",mountpoint="$MOUNTPOINT"} 1```

Fixes #45

limed/nubis-puppet-storage,tinnightcap/nubis-puppet-storage,Nubisproject/nubis-puppet-storage