Disable docker and alias to podman in FCOS ignition

Signed-off-by: Jason Greene <jason.greene@redhat.com>

pkg/machine/ignition.go

@@ -89,6 +89,18 @@ ExecStart=/bin/sh -c '/usr/bin/echo Ready >/dev/%s'
 [Install]
 RequiredBy=multi-user.target
 `
+	overlay := `[Unit]
+Description=Overlay /usr/bin mount
+
+[Mount]
+Type=overlay
+What=overlay
+Where=/usr/bin
+Options=lowerdir=/opt/bin:/usr/bin
+
+[Install]
+WantedBy=multi-user.target
+ `
 	_ = ready
 	ignSystemd := Systemd{
 		Units: []Unit{
@@ -101,6 +113,15 @@ RequiredBy=multi-user.target
 				Name:     "ready.service",
 				Contents: strToPtr(fmt.Sprintf(ready, "vport1p1", "vport1p1")),
 			},
+			{
+				Name: "docker.service",
+				Mask: boolToPtr(true),
+			},
+			{
+				Enabled:  boolToPtr(true),
+				Name:     "usr-bin.mount",
+				Contents: &overlay,
+			},
 		}}
 	ignConfig := Config{
 		Ignition: ignVersion,
@@ -253,5 +274,16 @@ func getLinks(usrName string) []Link {
 			Hard:   boolToPtr(false),
 			Target: "/home/" + usrName + "/.config/systemd/user/linger-example.service",
 		},
+	}, {
+		Node: Node{
+			Group:     getNodeGrp("root"),
+			Path:      "/opt/bin/docker",
+			User:      getNodeUsr("root"),
+			Overwrite: boolToPtr(true),
+		},
+		LinkEmbedded1: LinkEmbedded1{
+			Hard:   boolToPtr(false),
+			Target: "/usr/bin/podman",
+		},
 	}}
 }