libvirt: VM diagnostics (v3 API only)

There is no formal definition for the VM diagnostics. For the
V2 API the diagnostics will be returned as they are today.

This will support backward compatibility with the existing API's.

Part of the blueprint v3-diagnostics

DocImpact

Change-Id: I4128e76622e73a40d25fb50b10b1c1ac710a5cc4
Optimize instance_floating_address_get_all

Removed one extra round-trip to a database
and iteration through 'fixed_ip_ids' list

Change-Id: I65febddbc48350da93179aee8ff3c4130a6671d4
filter: add per-aggregate filter to configure disk_allocation_ratio

Adds a filter AggregateDiskFilter which provides the ability to
read from aggregates metadata the "disk_allocation_ratio".

DocImpact
Implements: blueprint per-aggregate-disk-allocation-ratio
Change-Id: I79d59fcdfb09e67ed6f12113615c673624b24a19
Merge "filter: add per-aggregate filter to configure disk_allocation_ratio"
Merge "libvirt: VM diagnostics (v3 API only)"
Merge "Optimize instance_floating_address_get_all"