* Temporarily backup StorPool volume before expunge
Sometimes the users delete the volumes by mistake. This enhancment
provides a solution to backup the volume before it's deleted. The user
will be able to see the snapshot in CloudStack UI/CLI and create only a
volume from it.
A task will check (by default on every 5mins) if the snapshots are
deleted from StorPool
Global settings to enable the delay delete option:
`storpool.delete.after.interval` - The interval (in seconds) after the StorPool snapshot will be deleted
`storpool.list.snapshots.delete.after.interval` - The interval (in seconds) to fetch the StorPool snapshots with deleteAfter flag
Minor fix when deleting snapshots
* added Apache licence
* addressed comments