tests: choose latest y-stream versioning for rhcos upgrade

The cincinatti graph is used to determine the latest OCP release. It
was assumed that only the latest node would have no upgrade path in
the graph but that is not the case. When upgrades are blocked, there
can be two nodes that no have upgrade path. We need to choose the
newest one in the upgrade test.

mantle/kola/tests/rhcos/upgrade.go

@@ -27,6 +27,7 @@ import (
 	cosa "github.com/coreos/coreos-assembler/pkg/builds"
 	coreosarch "github.com/coreos/stream-metadata-go/arch"
 
+	"github.com/coreos/go-semver/semver"
 	"github.com/coreos/mantle/kola"
 	"github.com/coreos/mantle/kola/cluster"
 	"github.com/coreos/mantle/kola/register"
@@ -358,8 +359,23 @@ func downloadLatestReleasedRHCOS(target string) (string, error) {
 		return
 	}(releaseIndex, unique)
 
+	// In cases where there is a blocked upgrade to a new Y-stream there can be
+	// two nodes that don't have an edge to upgrade to. This is generally the
+	// latest 4.Y-1.Z and the latest 4.Y.Z. Choose the latest 4.Y.Z
+	latest := difference[0]
+	if len(difference) == 2 {
+		vA := semver.New(graph.Nodes[difference[0]].Version)
+		vB := semver.New(graph.Nodes[difference[1]].Version)
+
+		if vA.LessThan(*vB) {
+			latest = difference[1]
+		} else {
+			latest = difference[0]
+		}
+	}
+
 	var ocpRelease *OcpRelease
-	latestOcpPayload := graph.Nodes[difference[0]].Payload
+	latestOcpPayload := graph.Nodes[latest].Payload
 	// oc should be included in cosa since https://github.com/coreos/coreos-assembler/pull/2777
 	cmd := exec.Command("/usr/bin/oc", "adm", "release", "info", latestOcpPayload, "-o", "json")
 	output, err := cmd.Output()