Don't try to dereferece NULL pointer.

Parallels Cloud Server has one serious discrepancy with libvirt:
libvirt stores domain configuration files in one place, and storage
files in other places (with the API of storage pools and storage volumes).
Parallels Cloud Server stores all domain data in a single directory,
for example, you may have domain with name fedora-15, which will be
located in '/var/parallels/fedora-15.pvm', and it's hard disk image will be
in '/var/parallels/fedora-15.pvm/harddisk1.hdd'.

I've decided to create storage driver, which produces pseudo-volumes
(xml files with volume description), and they will be 'converted' to
real disk images after attaching to a VM.

So if someone creates VM with one hard disk using virt-manager,
at first virt-manager creates a new volume, and then defines a
domain. We can lookup a volume by path in XML domain definition
and find out location of new domain and size of its hard disk.
Signed-off-by: NDmitry Guryanov <dguryanov@parallels.com>

Add functions for create/shutdown/destroy and suspend/resume domain.
Signed-off-by: NDmitry Guryanov <dguryanov@parallels.com>

Parallels driver is 'stateless', like vmware or openvz drivers.
It collects information about domains during startup using
command-line utility prlctl. VMs in Parallels are identified by UUIDs
or unique names, which can be used as respective fields in
virDomainDef structure. Currently only basic info, like
description, virtual cpus number and memory amount, is implemented.
Querying devices information will be added in the next patches.

Parallels doesn't support non-persistent domains - you can't run
a domain having only disk image, it must always be registered
in system.

Functions for querying domain info have been just copied from
test driver with some changes - they extract needed data from
previously created list of virDomainObj objects.
Signed-off-by: NDmitry Guryanov <dguryanov@parallels.com>