Restore instance flavor info when driver finish_migration fails

when instance resize, it will call finish_migration at last to create
new instance and destroy old instance. If driver layer has problem in
create new instance, the instance will be set to 'ERROR' state.

we are able to use reset-state --active to reset the instance and use it
but the instance information is set to new flavor
and not reverted to old one

Change-Id: I5961260f50e7893c7bf03e329e06edfd4f295640
Closes-Bug: #1296519
libvirt: add support for per-vCPU pinning in guest XML

Expand LibvirtConfigGuestCPUTune to allow setting of a
cpu mask per-vCPU

Blueprint: virt-driver-cpu-pinning
Change-Id: I547be6c7da4e3ebc9759f8310cb6282ac4b2f50c
libvirt: add support for memory backing parameters

Add a libvirt config class for dealing with the XML elements
under the <memoryBacking> section of the guest schema.

Blueprint: virt-driver-large-pages
Change-Id: Icd89508671a8951bed480b901b2d12d44ebb7cab
Merge "Restore instance flavor info when driver finish_migration fails"
Merge "libvirt: add support for per-vCPU pinning in guest XML"
Merge "libvirt: add support for memory backing parameters"