implement local volumes support

Add code, need for attaching volumes to the VMs and
implement local volumes support.
add ISCSI volumes support

Add ISCSI volume driver, the code is copy-pasted from
libvirt nova driver.
set openstack's guest device name as 'friendly_name'

Let's use guest device name from openstack as friendly_name,
so we can easily identify device on disconnecting.
disconnect volumes on instance destroy

On instance destroy we need to disconnect all volumes.
Implemented for lolca volumes only.
add get_used_block_devices function

Add function, which returns list of all host block
devices, attached to VEs. Unfortunately, PCS creates
DiskDescriptior.xml for each physical devices, and the only
way to get path to real device is to parse it (suing ploop
tool is more convenient).
find device to remove by path, not by name

It's more reliable to find device to remove by path
to the block device, instead of mount_device from openstack.
add support of detaching ISCSI volumes

Code mostly taken from libvirt's driver,
thank them very much for it!