Add backwards-compatibility for flags passed to plugins (#2479)

* update plugin server to ignore unknown flags during parse

Signed-off-by: Steve Kriss <krisss@vmware.com>

pkg/plugin/framework/server.go

@@ -103,6 +103,7 @@ func (s *server) BindFlags(flags *pflag.FlagSet) Server {
 	flags.Var(s.logLevelFlag, "log-level", fmt.Sprintf("the level at which to log. Valid values are %s.", strings.Join(s.logLevelFlag.AllowedValues(), ", ")))
 	flags.Var(s.featureSet, "features", "list of feature flags for this plugin")
 	s.flagSet = flags
+	s.flagSet.ParseErrorsWhitelist.UnknownFlags = true
 
 	return s
 }