Add support for instance vif traffic control.

Part 2 for blueprint quota-instance-resource, by adding exposed params
"vif_inbound_average, vif_inbound_burst, vif_inbound_peak,
vif_outbound_average, vif_outbound_burst, vif_outbound_peak" through
nova flavor-set, user can implement instance net traffic control policy.
for example:
nova flavor-set m1.medium set vif_inbound_average=10240000,
then the max inbound speed is 10MB/s. The usecase details of other params
will be noted on openstack-manuals.

Partly implement blueprint quota-instance-resource
DocImpact
original reviews https://review.openstack.org/#/c/14151/

Change-Id: I9934daadbf0e136e88530f5c23b556d070395bd0
Live migration with an auto selection of dest

Add ability to let scheduler decide on target host during live migration.

Implements: blueprint live-migration-scheduling
Change-Id: Id596fa3a0ef2b1b5faf854e4b4557b3c4b413e39
Merge "Live migration with an auto selection of dest"
Merge "Add support for instance vif traffic control."