Add scheduler plugin execution duration metric.

Address comments

Sample metrics

Use rand.Intn and some cleanup

pkg/scheduler/framework/v1alpha1/interface_test.go

@@ -74,3 +74,19 @@ func TestStatus(t *testing.T) {
 		}
 	}
 }
+
+// The String() method relies on the value and order of the status codes to function properly.
+func TestStatusCodes(t *testing.T) {
+	assertStatusCode(t, Success, 0)
+	assertStatusCode(t, Error, 1)
+	assertStatusCode(t, Unschedulable, 2)
+	assertStatusCode(t, UnschedulableAndUnresolvable, 3)
+	assertStatusCode(t, Wait, 4)
+	assertStatusCode(t, Skip, 5)
+}
+
+func assertStatusCode(t *testing.T, code Code, value int) {
+	if int(code) != value {
+		t.Errorf("Status code %q should have a value of %v but got %v", code.String(), value, int(code))
+	}
+}