Update QUANTUM_PLUGIN_CONFIG for N1K cisco plugin

when deploying n1k cisco plugin make sure to update the quantum_plugin_config
so the plugin is loaded appropriately. Since grizzly uses multi config,
only do this for n1k plugin which uses single config and let other plugin
use the default behavior.

Change-Id: I3a360e991c954570b729b547ef8b00d4eebd4a39
Merge "Update QUANTUM_PLUGIN_CONFIG for N1K cisco plugin" into stable/grizzly