ntp: fix config module schema to allow empty ntp config

Fix three things related to the ntp module:
  1. Fix invalid cloud-config schema in the integration test which
     provided empty dicts instead of emptylists for pools and servers
  2. Correct logic in the ntp module to allow support for the minimal
     cloud-config 'ntp:' without raising a RuntimeError. Docs and schema
     definitions already describe that cloud-config's ntp can be empty.
     An ntp configuration with neither pools nor servers will be
     configured with a default set of ntp pools. As such, the ntp module
     now officially allows the following ntp cloud-configs:
     - ntp:
     - ntp: {}
     - ntp:
         servers: []
         pools: []
  3. Add a simple unit test which validates all cloud-config provided to
      our integration tests to ensure it adheres to any defined module
      schema so as more jsonschema definitions are added, we validate our
      integration test configs.

LP: #1724951

1 files changed, 12 insertions, 11 deletions

diff --git a/tests/unittests/test_handler/test_handler_ntp.py b/tests/unittests/test_handler/test_handler_ntp.py
index 4f291248..3abe5786 100644
--- a/tests/unittests/test_handler/test_handler_ntp.py
+++ b/tests/unittests/test_handler/test_handler_ntp.py
@@ -293,23 +293,24 @@ class TestNtp(FilesystemMockingTestCase):
 
     def test_ntp_handler_schema_validation_allows_empty_ntp_config(self):
         """Ntp schema validation allows for an empty ntp: configuration."""
-        invalid_config = {'ntp': {}}
+        valid_empty_configs = [{'ntp': {}}, {'ntp': None}]
         distro = 'ubuntu'
         cc = self._get_cloud(distro)
         ntp_conf = os.path.join(self.new_root, 'ntp.conf')
         with open('{0}.tmpl'.format(ntp_conf), 'wb') as stream:
             stream.write(NTP_TEMPLATE)
-        with mock.patch('cloudinit.config.cc_ntp.NTP_CONF', ntp_conf):
-            cc_ntp.handle('cc_ntp', invalid_config, cc, None, [])
+        for valid_empty_config in valid_empty_configs:
+            with mock.patch('cloudinit.config.cc_ntp.NTP_CONF', ntp_conf):
+                cc_ntp.handle('cc_ntp', valid_empty_config, cc, None, [])
+            with open(ntp_conf) as stream:
+                content = stream.read()
+            default_pools = [
+                "{0}.{1}.pool.ntp.org".format(x, distro)
+                for x in range(0, cc_ntp.NR_POOL_SERVERS)]
+            self.assertEqual(
+                "servers []\npools {0}\n".format(default_pools),
+                content)
         self.assertNotIn('Invalid config:', self.logs.getvalue())
-        with open(ntp_conf) as stream:
-            content = stream.read()
-        default_pools = [
-            "{0}.{1}.pool.ntp.org".format(x, distro)
-            for x in range(0, cc_ntp.NR_POOL_SERVERS)]
-        self.assertEqual(
-            "servers []\npools {0}\n".format(default_pools),
-            content)
 
     @skipIf(_missing_jsonschema_dep, "No python-jsonschema dependency")
     def test_ntp_handler_schema_validation_warns_non_string_item_type(self):