Allow OVS default veth MTU to be configured.

In some environments where a packet is dropped when a VLAN tag is
added to the packet, you need to increase the MTU size of veth
interfaces to 1504.

Fixes: bug #1075336
Change-Id: I4f03b4cdc571a462096d419d6dd8324cf096156b
Service Type Framework refactoring

implements blueprint service-type-framework-cleanup

* Defines logic and API for ServiceProvider - read-only entity
that admins provide in configuration and which is stored in memory
* ServiceType entity which maps to ServiceOfferings in new terms
is removed for now.
* Routed service insertion fixed to not to refer to service providers.
* In case configuration changes and some service providers are removed
then the resources must be cleanup in a special way (undeploy logical
resources). This is a matter of future work
* Add migration.

Change-Id: I400ad8f544ec8bdc7d2efb597c995f284ff05829
Merge "Allow OVS default veth MTU to be configured."
Merge "Service Type Framework refactoring"