Make xenapi agent code use Instance object for updates

This makes the agent code use the Instance object that it is passed
to do the updates, instead of calling back to the old-style virtapi
instance_update() method.

Related to blueprint virt-objects-juno

Change-Id: Ied8891c974970a25f135a88303789d0c074741ee
Convert xenapi/vmops uses of instance_update to objects

This converts uses of the old instance_update() conductor method
to use the instance object in xenapi/vmops.

Related to blueprint virt-objects-juno

Change-Id: I5fab06934a7f3e7426631bb75eafe8b0d4b0806d
Make vmwareapi/vmops use Instance object for updates

This converts the one use of virtapi.instance_update() in vmops to
use the Instance object instead of the old conductor method.
Unfortunately, the affected method was apparently not tested at all,
so this adds a simple test for it.

Related to blueprint virt-objects-juno

Change-Id: I21ed4903a0c8d98c8776d358d8273077cd979fdf
Make libvirt driver use instance object for updates

This makes the libvirt driver use the Instance object for updates
instead of using the old raw conductor instance_update() method.

Related to blueprint virt-objects-juno

Change-Id: Ic25b2dc21dbc0038699f5fc33dd69334821abfc8
Merge "Make xenapi agent code use Instance object for updates"
Merge "Convert xenapi/vmops uses of instance_update to objects"
Merge "Make vmwareapi/vmops use Instance object for updates"
Merge "Make libvirt driver use instance object for updates"