parallels: add disks correctly

parallels: add disks correctly

Disks support in this driver was implemented with an assumption,
that disk images can't be created by hand, without VM. So
complex storage driver was implemented with workaround.

This is not true, we can create new disks using ploop tool.
So the first step to reimplement disks support in parallels
driver is to do not use information from the storage driver,
until we will implement VIR_STORAGE_TYPE_VOLUME disks.

So after this patch disks can be added in the same way as
in any other driver: you create a disk image and then add
an entry to the XML definition of the domain with path to that
image file, for example:

<disk type='file' device='disk'>
  <driver type='ploop'/>
  <source file='/storage/harddisk1.hdd'/>
  <target dev='sda' bus='sata'/>
  <address type='drive' controller='0' bus='0' target='0' unit='0'/>
</disk>

This patch makes parallels storage driver useless, but I'll fix it
later. Now you can create an image by hand, using ploop tool,
and then add it to some domain.

Signed-off-by: Dmitry Guryanov <dguryanov@parallels.com>