vdsm: [REFACTORING] libvirtvm.py bye bye

In order to start with the refactoring as a first step we'll get rid of
libvirtvm.py and merge vm.py into libvirtvm.py and named this whole thing
vm.py

Additionally Vm and LibvirtVm have been merged into one and there's now
only a class Vm.
Also devices have been renamed from LibvirtVmDevice to VmDevice
for simplicity.

Change-Id: I5ab8e2bc264b2a03eb21263d9faee1f55db109c8
Signed-off-by: Vinzenz Feenstra <vfeenstr@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/14203
Tested-by: Giuseppe Vallarelli <gvallare@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>