New configuration option is added to the nsx-v3 plugin: switching_profiles.
It will contain a list of switching profiles uuids that will be added to
NSX ports created by neutron.
The configuration is global or per availability zone.
In case the port should contain a different profile of some type,
the port-specific profile will be used, since the backend takes the last
one of each type.
Change-Id: Ifa1dba2250b224201e6f81816feb536a35b642a5