net: ubuntu focal prioritize netplan over eni even if both present

[blackboxsw]

On Focal and later, Ubuntu will prioritize netplan renderer before eni, even if ifupdown

and netplan are both installed. ENI on Bionic and later is considered an unsupported
configuration and so cloud-init should generally prefer netplan to eni rendering because
/etc/network/interfaces config file on many cloud images disables including cloud-init's
/etc/network/interfaces.d/50-cloud-init.cfg file.

Ubuntu series-specific changes may be applied to Bionic and Eoan, but further
discussion is warranted about the best approach on released series.

LP: #1867029

[raharper]

Let's add a unittest for this.

+    @mock.patch("cloudinit.net.renderers.netplan.available")
+    @mock.patch("cloudinit.net.renderers.sysconfig.available")
+    @mock.patch("cloudinit.net.renderers.sysconfig.available_sysconfig")
+    @mock.patch("cloudinit.net.renderers.sysconfig.available_nm")
+    @mock.patch("cloudinit.net.renderers.eni.available")
+    @mock.patch("cloudinit.net.renderers.sysconfig.util.get_linux_distro")
+    def test_netplan_selected_with_ifupdown_installed(self, m_distro,
+                                                            m_eni, m_sys_nm,
+                                                            m_sys_scfg,
+                                                            m_sys_avail,
+                                                            m_netplan):
+        """default policy selects netplan over eni when both installed."""
+
+        # Ubuntu with eni and netplan installed
+        m_netplan.return_value = True     # netplan is installed
+        m_eni.return_value = True         # ifupdown is installed
+        m_sys_scfg.return_value = False   # no sysconfig/ifup/ifdown
+        m_sys_nm.return_value = False     # no network-manager
+        m_sys_avail.return_value = False  # no sysconfig on Ubuntu
+        m_distro.return_value = ('ubuntu', None, None)
+        priority = renderers.DEFAULT_PRIORITY
+        self.assertEqual('netplan', renderers.select(priority=priority)[0])
+

[blackboxsw]

Added some pytests for both renderers.select() and ./tools/render-cloudcfg

[powersj]

@blackboxsw land and upload please