Drop support for Python 2 unicode string literals in YAML renderer

[terminalmage]

In earlier releases, the below was considered valid usage in Python 2, assuming that data was a dictionary containing keys/values which are unicode types:

/etc/foo.conf:
  file.managed:
    - source: salt://foo.conf.jinja
    - template: jinja
    - context:
        data: {{ data }}

Jinja will render the unicode string types in Python 2 with the "u" prefix (e.g. {u'foo': u'bar'}. While not valid YAML, earlier releases would successfully load these values.

This pull request drops this support, effective in the upcoming Fluorine release. Instead, it will now be necessary to use Jinja's "tojson" filter.

/etc/foo.conf:
  file.managed:
    - source: salt://foo.conf.jinja
    - template: jinja
    - context:
        data: {{ data|tojson }}

The "tojson" filter was added to Jinja in version 2.9, but several LTS releases (RHEL 7, Ubuntu 14.04, etc.) ship with earlier versions in their repositories. Therefore, this PR also adds an implementation of this filter, which will be used if Jinja doesn't already provide it (when it does, the upstream version of the filter will be used).

These changes allow Salt's custom YAML SafeLoader to use the libyaml versions of PyYAML's SafeLoader and SafeDumper (i.e. yaml.CSafeLoader and yaml.CSafeDumper) if PyYAML was built with libyaml support.

Thanks to @jacksontj for working with me on this.

[terminalmage]

My new integration test doesn't take into account dict iteration order differences. Derp. Fixing this as well as a lint violation, and there appear to be some other related failures.

[terminalmage]

OK, the necessary tests have been updated. I also have deprecated the json_encode_list and json_encode_dict filters, as they don't emit actual JSON, and are superseded by the tojson filter.

[isbm]

@terminalmage thanks 😉

[terminalmage]

I backported just the tojson filter to 2018.3 in #48339. I've updated the docs I wrote for this filter to reflect that.

This PR should be good to merge pending test results.

[rallytime]

@terminalmage This is failing one test: https://jenkins.saltstack.com/job/PR/job/salt-pr-linode-cent7-py3/6075/

[terminalmage]

@rallytime that should be fixed now. Apparently the jinja sort filter doesn't, you know, sort anything.