NetApp: E-Series remove snapshot limitations

NetApp: E-Series remove snapshot limitations

The E-Series backend does not allow snapshots defined under a snapshot
group to be deleted out of order. Only the oldest snapshot image may
be deleted. In order to work around this behavior, we would only define
a single snapshot on each snapshot group. Unfortunately, this would
limit the total number of snapshots to a total of 4 per volume.

In order to remove this limitation without causing deletion errors
when a newer snapshot is deleted, a soft-delete was implemented that
will remove the snapshot from Cinder management and purge the
snapshot from the backend once other dependent snapshots have been
deleted.

In order to ensure that our clone operations have a snapshot group
available, one of the 4 snapshot groups that can be defined on a
volume will be reserved for clone operations and will not be
allowed to be utilized for snapshot creation. This will limit the
total number of snapshots supported per volume to a maximum of 96.

The new 1.4 version of the WebServices proxy is required in order
to support the full snapshot behavior. Since snapshots are such
an integral part of the driver, 1.4 is now required for running
the driver with this release.

Co-Authored-By: Erik Johannes <erik.johannes@netapp.com>
Change-Id: Ie097743b167c1086ecf0536ad696786bdcd241b2