When the service insertion service plugin is configured without the nsx driver
port creation (and instances deployment) are failing because there is no
service insertion security group.
This patch make sure the nsx plugin knows the service insertion is disabled
in this case.
Depends-on: I4e7027cd456d7b16bb0c6136d9a556ad11246219
Change-Id: Idd7d4ccd1d7af8a6852803db00a3507f20d5f5a4