NetApp: Fix volume extend with E-Series

NetApp: Fix volume extend with E-Series

Thin provisioned volumes were being converted to thick provisioned
volumes by extend_volume. When thin provisioning support was added,
the extend_volume method was not updated to use the correct API
for performing the capacity expansion operation.

This patch changes the volume extension strategy when a volume is
thin provisioned to use the correct API. With a thick provisioned
volume, a clone will be created with the new capacity, and the old
volume removed, but a thin provisioned volume's capacity can simply
be expanded directly, because that is merely the capacity that the user
sees, as opposed to the backend provisioned capacity.

Closes-Bug: 1493874
Change-Id: Iec25f29381d5fba3409d1de83bf6816ae1a9ac22