Fix of wrong neutron.conf parameter for NSX plugin

Remove line "service_plugins=" from generated neutron.conf
when deploying with NSX plugin, cause deployment fails otherwise.

Change-Id: Ibe6e8a27fbf2c57e3ac10a52663b0d4496e4c933
Closes-bug: #1362317
Merge "Fix of wrong neutron.conf parameter for NSX plugin"