Compute Add build_instance hook in compute manager

The build_instance hook provides a hook close to the actual spawn
of an instance. It distinguishes itself from the create_instance
hook because, in the case of a successful build, the instance will
exist on the hypervisor when the build_instance post hook is
called, instead of simply just being scheduled as is the case with
the create_instance post hook. This is useful as some details may
not be available until after scheduling.

Co-Authored-By: Corey Wright <corey.wright@rackspace.com>
Change-Id: Ic12abf6315bbc6b010b8222ef296ec65cb4b4f95
Libvirt: Fsfreeze during live-snapshot of qemu/kvm instances

Currently it is required to execute fsfreeze command manually before
taking snapshots of active instances, otherwise the snapshot may be
inconsistent. When qemu-guest-agent is installed in a kvm instance,
we can request the instance to fsfreeze via libvirt's fsFreeze API
which is introduced in libvirt 1.2.5. To utilize this feature,
the image metadata must have 'os_require_quiesce=yes' property.
'hw_qemu_guest_agent=yes' is also needed to enable qemu-guest-agent.

Implements: blueprint quiesced-image-snapshots-with-qemu-guest-agent
Change-Id: I137efe00839ae0cb35e142b0c8f8d75ae61cfb64
Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama@hds.com>
Merge "Libvirt: Fsfreeze during live-snapshot of qemu/kvm instances"
Merge "Compute Add build_instance hook in compute manager"