Add python3 install

ignition/base-install-python3.bu

@@ -0,0 +1,25 @@
+variant: fcos
+version: 1.6.0
+
+systemd:
+  units:
+    # Install Python3
+    - name: rpm-ostree-install-python3.service
+      enabled: true
+      contents: |
+        [Unit]
+        Description=Install Python3
+        Wants=network-online.target
+        After=ignition-start-config.service
+        Before=zincati.service
+        ConditionPathExists=!/var/lib/%N.stamp
+
+        [Service]
+        Type=oneshot
+        RemainAfterExit=yes
+        ExecStart=/usr/bin/rpm-ostree install python3
+        ExecStart=/usr/bin/touch /var/lib/%N.stamp
+        ExecStart=/usr/bin/systemctl --no-block reboot
+
+        [Install]
+        WantedBy=multi-user.target