kola: support passing local OCI archives to --oscontainer

As part of openshift/os#799, we'll want to
be able to run tests against the layered image. We want to be able to
do that by pointing at the local file instead of having to push it to a
registry first (which in the pipeline usually happens at the end).

mantle/kola/harness.go

@@ -1843,8 +1843,22 @@ func runTest(h *harness.H, t *register.Test, pltfrm string, flight platform.Flig
 		if CosaBuild == nil {
 			h.Fatalf("Requested oscontainer pivot, but no cosa build found")
 		}
+		rebase_arg := Options.OSContainer
+		// if it looks like a path to an OCI archive, then copy it into the system
+		if strings.HasSuffix(Options.OSContainer, ".ociarchive") {
+			if err := cluster.DropFile(tcluster.Machines(), Options.OSContainer); err != nil {
+				h.Fatalf("dropping oscontainer file: %v", err)
+			}
+			// put it someplace rpm-ostree can access it; ideally we'd generalize DropFile
+			// to take a destination path instead
+			remote_file := filepath.Base(Options.OSContainer)
+			for _, m := range tcluster.Machines() {
+				tcluster.RunCmdSyncf(m, "mv -Z /home/core/%s /var/tmp/", remote_file)
+			}
+			rebase_arg = fmt.Sprintf("ostree-unverified-image:oci-archive:/var/tmp/%s", remote_file)
+		}
 		for _, m := range tcluster.Machines() {
-			tcluster.RunCmdSyncf(m, "sudo rpm-ostree rebase --experimental %s", Options.OSContainer)
+			tcluster.RunCmdSyncf(m, "sudo rpm-ostree rebase --experimental %s", rebase_arg)
 			m.Reboot()
 		}
 	}