Add schema to apt configure config (#357)

Create a schema object for the `apt_configure` module and
validate this schema in the `handle`  function of the module.

There are some considerations regarding this PR:

* The `primary` and `security` keys have the exact same properties. I
  tried to eliminate this redundancy by moving their properties to a
  common place and then just referencing it for both security and
  primary. Similar to what is documented here:
    https://json-schema.org/understanding-json-schema/structuring.html
  under the `Reuse` paragraph.  However, this approach does not work,
  because the `#` pointer goes to the beginning of the file, which is
  a python module instead of a json file, not allowing the pointer to
  find the correct definition. What I did was to create a separate dict
  for the mirror config and reuse it for primary and security, but
  maybe there are better approaches to do that.
* There was no documentation for the config `debconf_selections`. I
  tried to infer what it supposed to do by looking at the code and the
  `debconf-set-selections`  manpage, but my description may not be
  accurate or complete.
* Add a _parse_description function to schema.py to render multi-line
  preformatted content instead of squashing all whitespace

LP: #1858884

1 files changed, 36 insertions, 0 deletions

diff --git a/tests/unittests/test_handler/test_schema.py b/tests/unittests/test_handler/test_schema.py
index 071b98bc..e19d13b8 100644
--- a/tests/unittests/test_handler/test_schema.py
+++ b/tests/unittests/test_handler/test_schema.py
@@ -24,6 +24,7 @@ class GetSchemaTest(CiTestCase):
         schema = get_schema()
         self.assertCountEqual(
             [
+                'cc_apt_configure',
                 'cc_bootcmd',
                 'cc_locale',
                 'cc_ntp',
@@ -289,6 +290,41 @@ class GetSchemaDocTest(CiTestCase):
             """),
             get_schema_doc(full_schema))
 
+    def test_get_schema_doc_properly_parse_description(self):
+        """get_schema_doc description properly formatted"""
+        full_schema = copy(self.required_schema)
+        full_schema.update(
+            {'properties': {
+                'p1': {
+                    'type': 'string',
+                    'description': dedent("""\
+                        This item
+                        has the
+                        following options:
+
+                          - option1
+                          - option2
+                          - option3
+
+                        The default value is
+                        option1""")
+                }
+            }}
+        )
+
+        self.assertIn(
+            dedent("""
+                **Config schema**:
+                    **p1:** (string) This item has the following options:
+
+                            - option1
+                            - option2
+                            - option3
+
+                    The default value is option1
+            """),
+            get_schema_doc(full_schema))
+
     def test_get_schema_doc_raises_key_errors(self):
         """get_schema_doc raises KeyErrors on missing keys."""
         for key in self.required_schema: