Bug 1536860

As a Datacenter Administrator, I want to receive alerts via SMTP, system logs, and in the Cockpit UI when out of space thresholds are being met, so that I know when to add more physical space or manage my data in other ways (i.e. remove, move).
This use case requires the following information:
(a) concept information related to available VDO monitoring functionality
-i.e. thin provisioning monitored (physical space)
-Used Percent is amount of physical space used by VDO 
(b) concept and task information that informs the Datacenter 
Administrator of available alerts/notifications and how to set alert notifications via SMTP
-usage, compression ratio, alerts
-more physical space is needed
-optional resolution by Datacenter Administrator is to remove unneeded data
(c) concept and task information that informs the Datacenter 
Administrator of available messaging and how to access, understand, and respond to system log messages 
(d) task information that informs the Datacenter Administrator how to 
access, understand, and respond to alerts/notifications in the Cockpit UI
-current scheme is:
Notify: more free space is required (80% but not less than 
2 TB)
Warn: system is near full (90%, but not less than 1 TB)
Critical: VMs should be paused and/or the file system 
should be modified to read-only mode (95%, but not less than 500 GB)