store images in different formats in pcs-glance-tool

Add ability to store images in different formats (which
qemu-img supports) to pcs-glance-tool.

If we store images in formats, which openstack supports from
scratch, them these image can be converted to volumes without
any effort, while converting image in ploop format to a volume
on different storage requires at least support of ploop in
qemu-img and probably modification of cinder code.

To upload image in a foreign format we simple mount ploop and
convert it to another format with qemu-img convert.
kill VE during terminate and hard reboot

No need to do ACPI shutdown during hard reboot and terminate.
fix unplug methods in vif.py

If VM device is not found - get_prl_dev returns None,
and in this case we can simply return.
compress images in cache with prlcompress

prlcompress is a tool, which compresses ploop images,
so that they will take less space and creation of the
instances will be faster. PCS uses it for storing ez
template caches.
move code, which downloads ploop to a separate method

Move code, which downloads ploop image from glance to a
separate method, so it will be easier to support other
image formats.
get image name from DiskDescriptor.xml

There is no need to store image name in glance image metadata,
because it can be obtained from DiskDescriptor.xml.
remove unneded debug info from spawn method
fix error handling in _compress_ploop and _uncompress_ploop
don't set pcs_image_name in pcs-glance-tool

pcs_image_name is not needed anymore, so don't set it.
return supported_instances in get_host_stats

supported_instances field is required for image_properties
filter, which is used once you set architecture, hypervisor_type
or vm_mode in image metadata. I'm going to use them to distinguish
containers from vm, when they stored in fireign formats.
distinguish containers and VMs by vm_mode

Since we're going to support foreign image types, it's needed
to use another way to distinguish containers and VMs, not
disk type.

We can use vm_mode, which is also used by image_properties
filter.

So let's rename both ploop-vm and ploop-container to ploop and
add vm_mode.
add support of foreign disk formats

Add class QemuTemplate, which converts disks to ploop format
using qemu-img tool.