Fix nova/network direct use of object modules

This replaces all uses of nova.objects.<module>.<object> with
nova.objects.<object> within nova/network and nova/tests/network.

Change-Id: I6438bcf47e06a401323ea708d5a44c69fa00e967
Partial-Blueprint: object-subclassing
Catch InvalidAggregateAction when deleting an aggregate

When an aggregate with 'host' attribute not empty is deleted,
InvalidAggregateAction exception will be raised, but this exception
is not handled.

Closes-Bug: #1303591
Change-Id: I4ef0c4a6008acea7e9769e93de79451cfbc0a0fa
Standardization of nova.image.API.download

Brings the wacky download method into the new nova.image.API object and
removes calls to nova.image.glance throughout the virt drivers that were
using various call signatures of glance.ImageService.download. Since
some of the wrapper objects that fetched image bits from Glance were
using the get and update methods of the former
nova.image.glance.GlanceImageService object, those calls were updated to
instead call the new, standardized nova.image.API methods of the same
name and call signature.

The final patch in this series will refactor the remaining direct use of
the nova.image.glance module, which are calls to
glance.generate_image_url() and glance.generate_glance_url().

Change-Id: Ib3a85d0875c06c4e54e4211bc2fb8ce3fe16161d
Partially-implements blueprint: standardize-nova-image
Merge "Catch InvalidAggregateAction when deleting an aggregate"
Merge "Standardization of nova.image.API.download"
Merge "Fix nova/network direct use of object modules"