schema cli: Add schema subcommand to cloud-init cli and cc_runcmd schema

This branch does a few things:
  - Add 'schema' subcommand to cloud-init CLI for validating
    cloud-config files against strict module jsonschema definitions
  - Add --annotate parameter to 'cloud-init schema' to annotate
    existing cloud-config file content with validation errors
  - Add jsonschema definition to cc_runcmd
  - Add unit test coverage for cc_runcmd
  - Update CLI capabilities documentation

This branch only imports development (and analyze) subparsers when the
specific subcommand is provided on the CLI to avoid adding costly unused
file imports during cloud-init system boot.

The schema command allows a person to quickly validate a cloud-config text
file against cloud-init's known module schemas to avoid costly roundtrips
deploying instances in their cloud of choice. As of this branch, only
cc_ntp and cc_runcmd cloud-config modules define schemas. Schema
validation will ignore all undefined config keys until all modules define
a strict schema.

To perform validation of runcmd and ntp sections of a cloud-config file:
$ cat > cloud.cfg <<EOF
runcmd: bogus
EOF
$ python -m cloudinit.cmd.main schema --config-file cloud.cfg

$ python -m cloudinit.cmd.main schema --config-file cloud.cfg \
  --annotate

Once jsonschema is defined for all ~55 cc modules, we will move this
schema subcommand up as a proper subcommand of the cloud-init CLI.

1 files changed, 54 insertions, 28 deletions

diff --git a/cloudinit/config/cc_runcmd.py b/cloudinit/config/cc_runcmd.py
index dfa8cb3d..7c3ccd41 100644
--- a/cloudinit/config/cc_runcmd.py
+++ b/cloudinit/config/cc_runcmd.py
@@ -6,41 +6,66 @@
 #
 # This file is part of cloud-init. See LICENSE file for license information.
 
-"""
-Runcmd
-------
-**Summary:** run commands
+"""Runcmd: run arbitrary commands at rc.local with output to the console"""
 
-Run arbitrary commands at a rc.local like level with output to the console.
-Each item can be either a list or a string. If the item is a list, it will be
-properly executed as if passed to ``execve()`` (with the first arg as the
-command). If the item is a string, it will be written to a file and interpreted
-using ``sh``.
-
-.. note::
-    all commands must be proper yaml, so you have to quote any characters yaml
-    would eat (':' can be problematic)
-
-**Internal name:** ``cc_runcmd``
-
-**Module frequency:** per instance
+from cloudinit.config.schema import validate_cloudconfig_schema
+from cloudinit.settings import PER_INSTANCE
+from cloudinit import util
 
-**Supported distros:** all
+import os
+from textwrap import dedent
 
-**Config keys**::
 
-    runcmd:
-        - [ ls, -l, / ]
-        - [ sh, -xc, "echo $(date) ': hello world!'" ]
-        - [ sh, -c, echo "=========hello world'=========" ]
-        - ls -l /root
-        - [ wget, "http://example.org", -O, /tmp/index.html ]
-"""
+# The schema definition for each cloud-config module is a strict contract for
+# describing supported configuration parameters for each cloud-config section.
+# It allows cloud-config to validate and alert users to invalid or ignored
+# configuration options before actually attempting to deploy with said
+# configuration.
 
+distros = ['all']
 
-import os
+schema = {
+    'id': 'cc_runcmd',
+    'name': 'Runcmd',
+    'title': 'Run arbitrary commands',
+    'description': dedent("""\
+        Run arbitrary commands at a rc.local like level with output to the
+        console. Each item can be either a list or a string. If the item is a
+        list, it will be properly executed as if passed to ``execve()`` (with
+        the first arg as the command). If the item is a string, it will be
+        written to a file and interpreted
+        using ``sh``.
 
-from cloudinit import util
+        .. note::
+        all commands must be proper yaml, so you have to quote any characters
+        yaml would eat (':' can be problematic)"""),
+    'distros': distros,
+    'examples': [dedent("""\
+        runcmd:
+            - [ ls, -l, / ]
+            - [ sh, -xc, "echo $(date) ': hello world!'" ]
+            - [ sh, -c, echo "=========hello world'=========" ]
+            - ls -l /root
+            - [ wget, "http://example.org", -O, /tmp/index.html ]
+    """)],
+    'frequency': PER_INSTANCE,
+    'type': 'object',
+    'properties': {
+        'runcmd': {
+            'type': 'array',
+            'items': {
+                'oneOf': [
+                    {'type': 'array', 'items': {'type': 'string'}},
+                    {'type': 'string'}]
+            },
+            'additionalItems': False,  # Reject items of non-string non-list
+            'additionalProperties': False,
+            'minItems': 1,
+            'required': [],
+            'uniqueItems': True
+        }
+    }
+}
 
 
 def handle(name, cfg, cloud, log, _args):
@@ -49,6 +74,7 @@ def handle(name, cfg, cloud, log, _args):
                    " no 'runcmd' key in configuration"), name)
         return
 
+    validate_cloudconfig_schema(cfg, schema)
     out_fn = os.path.join(cloud.get_ipath('scripts'), "runcmd")
     cmd = cfg["runcmd"]
     try: