Add Ignorable flag to extender

Ignore extender in generic scheduler

Add test to verify the ignorable flag

Fix warning msg

pkg/scheduler/algorithm/scheduler_interface.go

@@ -64,6 +64,10 @@ type SchedulerExtender interface {
 
 	// SupportsPreemption returns if the scheduler extender support preemption or not.
 	SupportsPreemption() bool
+
+	// IsIgnorable returns true indicates scheduling should not fail when this extender
+	// is unavailable. This gives scheduler ability to fail fast and tolerate non-critical extenders as well.
+	IsIgnorable() bool
 }
 
 // ScheduleAlgorithm is an interface implemented by things that know how to schedule pods