fix(snapd): ubuntu do not snap refresh when snap absent

No longer call snap refresh when cloud-config user-data
specifies upgade_packages:true and custom Ubuntu images
do not have snapd package installed

LP: #2064300

cloudinit/distros/ubuntu.py

@@ -40,7 +40,8 @@ def __init__(self, name, cfg, paths):
 
     def package_command(self, command, args=None, pkgs=None):
         super().package_command(command, args, pkgs)
-        self.snap.upgrade_packages()
+        if self.snap.available():
+            self.snap.upgrade_packages()
 
     @property
     def preferred_ntp_clients(self):

tests/unittests/distros/test_ubuntu.py

@@ -0,0 +1,32 @@
+# This file is part of cloud-init. See LICENSE file for license information.
+import pytest
+
+from cloudinit.distros import fetch
+
+
+class TestPackageCommand:
+    @pytest.mark.parametrize("snap_available", (True, False))
+    def test_package_command_only_refresh_snap_when_available(
+        self, snap_available, mocker
+    ):
+        """Avoid calls to snap refresh when snap command not available."""
+        m_snap_available = mocker.patch(
+            "cloudinit.distros.ubuntu.Snap.available",
+            return_value=snap_available,
+        )
+        m_snap_upgrade_packges = mocker.patch(
+            "cloudinit.distros.ubuntu.Snap.upgrade_packages",
+            return_value=snap_available,
+        )
+        m_apt_run_package_command = mocker.patch(
+            "cloudinit.distros.package_management.apt.Apt.run_package_command",
+        )
+        cls = fetch("ubuntu")
+        distro = cls("ubuntu", {}, None)
+        distro.package_command("upgrade")
+        m_apt_run_package_command.assert_called_once_with("upgrade")
+        m_snap_available.assert_called_once()
+        if snap_available:
+            m_snap_upgrade_packges.assert_called_once()
+        else:
+            m_snap_upgrade_packges.assert_not_called()