(PDK-1112) Create json schema to validate pdk config file

[glennsarti]

• Address TODOs
• Finish yard docs for methods
• What happens if the file is not valid BEFORE the PDK tries to read it? We can never save it due to the validation.

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Previously the Config Namespace class conflated a few concepts together and had
less than ideal method naming. This commit:

• Changes the name of a namespace value to a namespace setting. This is because
  the class held more than just a value, such as the default value and
  validators. Therefore it made more sense to call it a a Namespace Setting.

• The namespace had an abstract method called parse_data which was passed both
  the data and the name to the file. This didn't make sense as the filename is
  all that's required, not the filename. The method was also renamed to
  parse_file which is more accurate name.

• The parse_file used to return an array of objects, but this create extra array
  objects during parsing. This commit changes the method to instead yield
  namespace setting objects. This will allow namespaces to create their own
  settings objects instead of only using the one.

• Refactors common file based namespace tests to an rspec shared example.

• Adds tests for assigning values to a setting

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Previously there was no formal schema, or a way to validate a schema, for
configuration settings. This commit adds two new namespace types, YAML and
JSON files with JSON schema validation.

These namespaces will also take a JSON Schema file and use that to provide
defaults and validation. Any settings NOT in the schema will not be visible in
the namespace, but will not be lost when saving the namespace to disk; That is
the namespace will only modify settings that are in the schema. This also
includes tests for any schema files, to ensure that they are indeed valid.

This commit adds a schema for the PDK analytics configuration.

This commit introduces a new setting type, JSONSchemaSetting which uses the
schema to validate and get default values for a setting from the schema.

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This commit adds the tests for the new schema based namespaces. This commit
also refactors common tests between JSON, YAML and non-schema namespaces into
rspec shared example groups.

Note that due to a bug in json-schema object, the tests fail on non-Windows
platforms.

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Unfortunately the json-schema gem fails to load filed based schema on Windows
due to URI encoding issues. Also the json-schema gem is abandoned so it get
fixed either, and other gems don't have support for old ruby 2.1. This commit
monkey patches the JSON Schema read_file method to munge the pathname on
Windows platforms.

This commit removes the test guards on non-Windows platforms.

[coveralls]

Coverage increased (+0.2%) to 92.258% when pulling c6411c3 on glennsarti:pdk-1112-config-schema into 378f22d on puppetlabs:master.

[scotje]

Looks good to me @glennsarti !