Live migrate each instance from one host to other hosts

Using the existing server live_migrate api, this new feature,
adds the ability for admins to live-migrate all running instances
from one host to other hosts. The patch implements the feature
for Nova API V2 and API V3.

Co-Authored-By: Cédric Soulas <cedric.soulas@cloudwatt.com>

Change-Id: Ie8dd1b66fb8eaefa6ff38752b1e4f46bab145820
Implements: blueprint host-servers-live-migrate
Use oslo.serialization

Since module `jsonutils` from common code is graduated in
`oslo.serialization`, we should remove code from oslo-incubator and use this
library.

Change-Id: Ia8b5ef598ff415cdde19f523a36a552918f9f94b
Merge "Live migrate each instance from one host to other hosts"
Merge "Use oslo.serialization"