Add ability for core plugin to implement advanced services

implements blueprint api-core-for-services

Add check for supported_extension_aliases in QuantumManager.
If core plugin supports certain service extension, then core plugin is
stored in service_plugins for the service type of this extension
so corresponding extension could set it as a controller for REST calls.

Change-Id: I9c883491f6f13770371e3444e7c17bd2164a7c07
make default transport type configurable nvp

Fixes bug 1179759

Change-Id: I8f644f2bc0d5d144f52e5ed0bd2e991503581ad2
Add missing unit test for NVP metadata_mode option

Note: I didn't squash this change in my patch that made the default
transport type configurable because this change was not in grizzly
and we do not want to backport it.

Change-Id: Ie71e5e56d1bed219caba74799cc2310ace987b8f
Merge "Add ability for core plugin to implement advanced services"