kola: fix requiredTag handling

If a test has both required tags and non-required tags, it would still be
activated if the user passed one of the non-required tags. But we want it
to only run if the one that's required was passed.

mantle/kola/harness.go

@@ -540,7 +540,7 @@ func filterTests(tests map[string]*register.Test, patterns []string, pltfrm stri
 		}
 
 		if t.RequiredTag != "" && // if the test has a required tag...
-			!tagMatch && // and that tag was not provided by the user...
+			!HasString(t.RequiredTag, positiveTags) && // and that tag was not provided by the user...
 			(!userTypedPattern || !nameMatch) { // and the user didn't request it by name...
 			continue // then skip it
 		}