Add flavor-manage to core for V3 API

Adds the flavor-manage plugin to the core list for the V3 API.
This is part of the process of adding all of the flavor related
extensions to core, with the exception of rxtx, as per the discussion
here: https://etherpad.openstack.org/p/NovaV3APICore

Partially implements blueprint nova-v3-api

DocImpact

Change-Id: Idbedce5cc5936abc52235cd40573c8fe841f24fe
Remove unnecessary steps for cold snapshots

Up until now when we created cold snapshots we were stopping the
instance, create an internal snapshot, extract the snapshot to a file
and then delete the internal snapshot before bringing up the instance.

If the instance is shut down, there's no concurrent writer, so the image
can be directly extracted without taking an internal snapshot first,
because the snapshot and the current state are the same.

In this patch the creation and deletion of the internal snapshot are
removed to eliminate the extra steps and optimize the creation of
snapshots a bit.

Closes-Bug: #1242819
Closes-Bug: #1247185

Change-Id: I429fa2e1e26aea321eecbf14edd11263fff525ae
domainEventRegisterAny called too often

Changeid I090765802bfe443440f16722bc7c43b6280fe56a fixes
bug #1240905 but introduced a bug whereby domainEventRegisterAny
is called on every call to _get_connection.

Change-Id: Ifafc6a4c172b1521d62988ccbb3a2f51a95e323f
Fixes: bug #1250135
Rename virtapi.instance_type_get to flavor_get

Renames the virtapi.instance_type_get method to flavor_get. Updates the
directly related tests and subclass implementations of VirtAPI.

This patch does not propagate to all related code like conductor API,
that will be handled in a later patch for the blueprint.

Part of bp flavor-instance-type-dedup

Change-Id: Ic47da9aa578d449a4ce542d2d017840f1a8132a7
More instance_type -> flavor renames in db.api

Renames the instance_type methods in db.api to flavor and converts the
tests to match. Updates doc strings where needed.

Note that this patch doesn't rename anything touching the db models for
instance types, that will be handled in a later patch for the blueprint.

Part of bp flavor-instance-type-dedup

Change-Id: I397421c9b34d295368999c5d085345409945151a
Cache Neutron Client for Admin Scenarios

Store a thread local copy of Neutron client for use with admin
tokens, this will prevent excessive calls to keystone to mint
new tokens and will enable reuse of the already set up client
for subsequent calls in this thread.

Change-Id: I6346281ca3516c31b195ce71942786d724e5e9df
Closes-Bug: #1250580
replace assertNotEquals with assertNotEqual

assertNotEquals will be deprecated in Python 3.

This is part of blueprint assertequal

Closes loose ends with assertEquals.

Change-Id: I5cd5c8ceb8b0232f1218d6f445d230c8747ac327
Merge "Remove unnecessary steps for cold snapshots"
Merge "domainEventRegisterAny called too often"
Merge "Rename virtapi.instance_type_get to flavor_get"
Merge "replace assertNotEquals with assertNotEqual"
Merge "Cache Neutron Client for Admin Scenarios"
Merge "Add flavor-manage to core for V3 API"
Merge "More instance_type -> flavor renames in db.api"