config: Improve the Provider matching to have a negated match #2140

This makes it easier to make classes of provider in the config.

fs/config.go

@@ -22,6 +22,9 @@ var (
 	// This is a function pointer to decouple the config
 	// implementation from the fs
 	CountError = func(err error) {}
+
+	// ConfigProvider is the config key used for provider options
+	ConfigProvider = "provider"
 )
 
 // ConfigInfo is filesystem config options