Change param "plugin config" of Neutron Server
Change param "plugin config" of Neutron Server

Changed param name from "plugin config" to "plugin_config"
because cluster param's key name can not be set with blank charactor.

Change-Id: I9c5276c7b8301b2df7d8441c7fc61a88aa27936f
Closes-Bug: #1508399

openstack/openstack-resource-agents