prometheus-operator: Fix unit test

Return when the test that wants error, errors out. This means the test
has passed and should not be proceeded further.

Signed-off-by: Suraj Deshmukh <suraj@kinvolk.io>

pkg/components/prometheus-operator/component_test.go

@@ -81,6 +81,10 @@ component "prometheus-operator" {
 
 			if tc.wantErr && !d.HasErrors() {
 				t.Fatal("wrong config should have returned an error")
+			} else if tc.wantErr && d.HasErrors() {
+				// This means that test has passed and there is no need to go forward, we can safely
+				// return.
+				return
 			}
 
 			m, err := c.RenderManifests()