FEATURE: PCI-4320 - revert pool-aware support from driver

backport Juno Cinder to Folsom Nova continued..

Revert pool-aware support from Netapp driver. AFAIK Folsom does
not support that. Folsom should be sending volume['host'] in
a form "HostA@BackendB#PoolC", but it contains only host.
Driver from the string should extract PoolC which is determines
the Netapp volume, where LUN should be created.

I have replace that code with a dummy hack to retrieve the volume
name from configuration "netapp_volume_list". This parameter
was optional and contained _list_ of volumes. I accept only
one volume now and the parameter is mandatory now.

On Cmode driver the options "netapp_volume_list" is not even there,
so I had to add it to driver init.