handle upgrade path and defaults

Ensure that `""` Scheduler Algorithm gets explicitly set to binpack on
upgrades or on API handling when user misses the value.

The scheduler already treats `""` value as binpack.  This PR merely
ensures that the operator API returns the effective value.

command/agent/command.go

@@ -285,6 +285,8 @@ func (c *Command) readConfig() *Config {
 		config.PluginDir = filepath.Join(config.DataDir, "plugins")
 	}
 
+	config.Server.DefaultSchedulerConfig.Canonicalize()
+
 	if !c.isValidConfig(config, cmdConfig) {
 		return nil
 	}