mantle/kola/harness: allow success if all tests are denylisted

This will allow us to denylist certain categories of tests and not
have the pipeline fail. See [1] for a real world example of why this
is useful.

[1] coreos/fedora-coreos-config@e983073

mantle/kola/harness.go

@@ -783,11 +783,16 @@ func runProvidedTests(testsBank map[string]*register.Test, patterns []string, mu
 			}
 		}
 
+		if len(tests) > 0 && suiteErr == harness.SuiteEmpty && allTestsDenyListed(tests) {
+			fmt.Printf("There are no tests to run because all tests are denylisted. Output in %v\n", outputDir)
+			return nil
+		}
 		if caughtTestError {
 			fmt.Printf("FAIL, output in %v\n", outputDir)
 		} else {
 			fmt.Printf("PASS, output in %v\n", outputDir)
 		}
+
 		return suiteErr
 	}
 
@@ -810,6 +815,20 @@ func runProvidedTests(testsBank map[string]*register.Test, patterns []string, mu
 	return firstRunErr
 }
 
+func allTestsDenyListed(tests map[string]*register.Test) bool {
+	for name := range tests {
+		isDenylisted, err := testIsDenyListed(name)
+		if err != nil {
+			plog.Warningf("Error while checking denylist for test:", err)
+			continue
+		}
+		if !isDenylisted {
+			return false
+		}
+	}
+	return true
+}
+
 func allTestsAllowRerunSuccess(testsBank map[string]*register.Test, testsToRerun, rerunSuccessTags []string) bool {
 	// No tags, we can return early
 	if len(rerunSuccessTags) == 0 {