CH release adds new way to associate resources with nsgroups by
creating specific tags on the resources.
We would like to support this feature in the plugin for better performance.
This patch make use of this feature to associate logical-ports with nsgroups
(Neutron ports with security-groups), for every LP-NSGroup association,
a special tag will be added to the LP.
The plugin will use this NSX feature only when supported by the NSX
version, and given that the designated boolean config option is set to True.
Change-Id: I2a802bc314d98dba9ecc54191fcbd7330f183e12
ddfb880d5a