Enables Quantum to support a number of different networking technologies (each supported by a specific plugin)

Currently Quantum only supports one plugin. The blueprint will enable Quantum to support a number of different networking technologies by using the same Quantum interface. The idea in general is to register a new plugin that will be a proxy for one or more existing plugins. This will enable hosts to run different Quantum agents - each agent will interface with its plugin in the same fashion as today.
The plugin will relay all of the Quantum commands to the backend plugins. The plugin will maintain a cross reference table for all of the ID's, that is, the plugin will allocate a UUID which will be used by the Quantum interface. This ID will be mapped to the ID allocated by the actual plugin (for example OVS plugin)
For example
User Plugin

network create -> plugin -> Allocate UUID A
                                                   for each registered plugin -> network create for plugin X
                                                                                                         Save X's UUID
                                                                                                    -> network create for plugin Y
                                                                                                         Save Y's UUID
                                                                                                    ...
                                                   UUID A = {UUIDY, UUID X, ...}
network UUID A <-

Now all updates to UUID A will be translated to the stored UUID's and relayed to the actual backend plugin.