Add Strict Metaschema Validation (#1101)

Improve schema validation.

This adds strict validation of config module definitions at testing
time, with plumbing included for future runtime validation. This
eliminates a class of bugs resulting from schemas that have definitions
that are incorrect, but get interpreted by jsonschema as
"additionalProperties" that are therefore ignored.

- Add strict meta-schema for jsonschema unit test validation
- Separate schema from module metadata structure
- Improve type annotations for various functions and data types

Cleanup:
- Remove unused jsonschema "required" elements 
- Eliminate manual memoization in schema.py:get_schema(),
        reference module.__doc__ directly

1 files changed, 6 insertions, 4 deletions

diff --git a/cloudinit/config/cc_resizefs.py b/cloudinit/config/cc_resizefs.py
index 990a6939..00bb7ae7 100644
--- a/cloudinit/config/cc_resizefs.py
+++ b/cloudinit/config/cc_resizefs.py
@@ -13,8 +13,7 @@ import os
 import stat
 from textwrap import dedent
 
-from cloudinit.config.schema import (
-    get_schema_doc, validate_cloudconfig_schema)
+from cloudinit.config.schema import get_meta_doc, validate_cloudconfig_schema
 from cloudinit.settings import PER_ALWAYS
 from cloudinit import subp
 from cloudinit import util
@@ -24,7 +23,7 @@ NOBLOCK = "noblock"
 frequency = PER_ALWAYS
 distros = ['all']
 
-schema = {
+meta = {
     'id': 'cc_resizefs',
     'name': 'Resizefs',
     'title': 'Resize filesystem',
@@ -42,6 +41,9 @@ schema = {
     'examples': [
         'resize_rootfs: false  # disable root filesystem resize operation'],
     'frequency': PER_ALWAYS,
+}
+
+schema = {
     'type': 'object',
     'properties': {
         'resize_rootfs': {
@@ -52,7 +54,7 @@ schema = {
     }
 }
 
-__doc__ = get_schema_doc(schema)  # Supplement python help()
+__doc__ = get_meta_doc(meta, schema)  # Supplement python help()
 
 
 def _resize_btrfs(mount_point, devpth):