Use strongerrors in provider implementations. (#403)

This ensures that we can catch certain types of errors from providers
and handle accordingly in the core. There is still more to do here to
improve that but this resolves an immediate need to know why a Delete
failed.

vic provider was not updated since I could not figure out where to get
this information.

providers/aws/fargate/cluster.go

@@ -10,6 +10,7 @@ import (
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/cloudwatchlogs"
 	"github.com/aws/aws-sdk-go/service/ecs"
+	"github.com/cpuguy83/strongerrors"
 	k8sTypes "k8s.io/apimachinery/pkg/types"
 )
 
@@ -272,7 +273,7 @@ func (c *Cluster) GetPod(namespace string, name string) (*Pod, error) {
 	tag := buildTaskDefinitionTag(c.name, namespace, name)
 	pod, ok := c.pods[tag]
 	if !ok {
-		return nil, fmt.Errorf("pod %s/%s is not found", namespace, name)
+		return nil, strongerrors.NotFound(fmt.Errorf("pod %s/%s is not found", namespace, name))
 	}
 
 	return pod, nil