[PATCH 0 of 2] pci passthrough: support "managed" pci device in xend for libvirt usage

[cyliu@suse.com]

One of our customers requests parallel pci passthrough functionality between xen
(xend and libxl) and kvm, including support managed host pci devices. A 
"managed" pci device will be made assignable before vm start  and reattach to 
its original dirver after vm shut off.

Currently, libvirt supports "managed=yes/no" options in pci device definition.
Qemu driver already supports managed pci devices, libxl driver will add that
support in libvirt source code. For xend driver, since it's stateful, libvirt
can't do much things because libvirt doesn't store much informtion and most
work is done by calling xend directly. Even "managed" option won't be stored if
xend doesn't support it. For that reason, this patch series tries to add code in
xend toolstack to support managed pci devices first, then libvirt can call xend
operations directly to support "managed" host pci devices. 

Syntax for managed pci device could be:
pci=['0000:00:1a.0,managed=1']

Please share your comments. Thanks!