certprovider-api: use correct format for "certificate_providers" field

[easwars]

The expected format for the certificate_providers field was wrong:

	"certificate_providers" : {
		"default": { 
			"plugin_bar" : {bar plugin config in JSON }
		},
		"foo": {
			"plugin_foo" : { foo plugin config in JSON }
		}
	}

The correct format is:

	"certificate_providers" : {
		"default": {
			"plugin_name": "plugin_bar",
			"config": { default plugin config in JSON }
		},
		"foo": {
			"plugin_name": "plugin_foo",
			"config": { foo plugin config in JSON }
		}
	}