Allow random cluster selection when no override (flyteorg#117)

In case there is no override in resource table, we should allow the code
to go through and apply non-label based weighted random selection.

Close flyteorg#481

flyteadmin/pkg/executioncluster/impl/random_cluster_selector.go

@@ -130,7 +130,6 @@ func (s RandomClusterSelector) GetTarget(ctx context.Context, spec *executionclu
 		if flyteAdminError, ok := err.(errors.FlyteAdminError); !ok || flyteAdminError.Code() != codes.NotFound {
 			return nil, err
 		}
-		return nil, err
 	}
 	var weightedRandomList random.WeightedRandomList
 	if resource != nil && resource.Attributes.GetExecutionClusterLabel() != nil {

flyteadmin/pkg/executioncluster/impl/random_cluster_selector_test.go

@@ -143,6 +143,16 @@ func TestRandomClusterSelectorGetTargetForDomainAndExecution2(t *testing.T) {
 }
 
 func TestRandomClusterSelectorGetRandomTarget(t *testing.T) {
+	cluster := getRandomClusterSelectorForTest(t)
+	target, err := cluster.GetTarget(context.Background(), &executioncluster.ExecutionTargetSpec{
+		Project: "",
+	})
+	assert.Nil(t, err)
+	assert.True(t, target.ID == "testcluster1" || target.ID == "testcluster2" || target.ID == "testcluster3")
+	assert.True(t, target.Enabled)
+}
+
+func TestRandomClusterSelectorGetRandomTargetUsingEmptySpec(t *testing.T) {
 	cluster := getRandomClusterSelectorForTest(t)
 	_, err := cluster.GetTarget(context.Background(), nil)
 	assert.NotNil(t, err)