mantle/podman.go: use RetryUntilTimeout in podman.workflow

The podman.workflow test has been failing on OpenStack, likely
because pulling the Fedora container takes too long. Use the
`RetryUntilTimeout` function to retry every minute for up to 15
minutes to allow sufficient time to pull the Fedora container.
In local testing, pulling the container on OpenStack took
approximately 5 minutes before succeeding.

See: coreos/fedora-coreos-tracker#1835

mantle/kola/tests/podman/podman.go

@@ -154,7 +154,7 @@ func podmanWorkflow(c cluster.TestCluster) {
 			return nil
 		}
 
-		if err := util.Retry(6, 10*time.Second, podIsRunning); err != nil {
+		if err := util.RetryUntilTimeout(15*time.Minute, 5*time.Minute, podIsRunning); err != nil {
 			c.Fatal("Pod is not running")
 		}
 	})