feat(cloud-init): support ubuntu_pro user-data (SC-1555)

In #cloud-config user-data, cloud-init will be deprecating the
ubuntu_advantage key in favor of ubuntu_pro to align with the
current product naming and branding.

To avoid tightly coupling ubuntu-pro-client with cloud-init
releases, add support for the new 'ubuntu_pro' config key and
retain support for the deprecated keys:
 - ubuntu-advantage
 - ubuntu_advantage

Since cloud-init doesn't target Ubuntu Xenial for stable release
updates (SRUs), the ubuntu-advantage/ubuntu_advantage keys must be
supported by cloud-init and ubuntu-pro-client in Xenial unless a
backport of latest cloud-init cc_ubuntu_advantage.py module is
published to Xenial.

lib/auto_attach.py

@@ -33,6 +33,11 @@
 
 LOG = logging.getLogger("ubuntupro.lib.auto_attach")
 
+# All known cloud-config keys which provide ubuntu pro configuration directives
+CLOUD_INIT_UA_KEYS = set(
+    ["ubuntu-advantage", "ubuntu_advantage", "ubuntu_pro"]
+)
+
 try:
     import cloudinit.stages as ci_stages  # type: ignore
 except ImportError:
@@ -54,10 +59,7 @@ def check_cloudinit_userdata_for_ua_info():
     if init is None:
         return False
 
-    if init.cfg and (
-        "ubuntu_advantage" in init.cfg.keys()
-        or "ubuntu-advantage" in init.cfg.keys()
-    ):
+    if init.cfg and CLOUD_INIT_UA_KEYS.intersection(init.cfg):
         return True
 
     return False

uaclient/tests/test_lib_auto_attach.py

@@ -41,6 +41,20 @@ def test_check_cloudinit_data_returns_false_if_no_cloudinit(
                     "cloud_config_modules": ["ubuntu-advantage", "test"],
                 },
             ),
+            (
+                True,
+                {
+                    "ubuntu_pro": {"token": "TOKEN"},
+                    "cloud_config_modules": ["ubuntu-advantage", "test"],
+                },
+            ),
+            (
+                True,
+                {
+                    "ubuntu-advantage": {"token": "TOKEN"},
+                    "cloud_config_modules": ["ubuntu-advantage", "test"],
+                },
+            ),
         ),
     )
     @mock.patch("lib.auto_attach.get_cloudinit_init_stage")