some structures still need `to_json` filter, with or without `use_yamlloader_old`

Description of Issue

In 2019.2.2, certain structures and values passed as pillar data (at least) result in the found unexpected ':' error on rendering, even with use_yamlloader_old enabled. In 2018.3.3, the failure case below works fine.

This is essentially the minimal case submitted in https://github.com/saltstack/salt/issues/52681#issuecomment-487609024.

Setup

#  Fail with state.apply w/ pillar='{"test": ["a:b"]}'
/etc/foo.conf:
  file.managed:
    - context:
        foo: {{ pillar.get('test', ["c:d"]) }}

Steps to Reproduce Issue

On master/minion running 2019.2.2, with or without use_yamlloader_old enabled:

[root@master1 /]# salt 3dedd8fe9f9f state.apply foo_state
3dedd8fe9f9f:
----------
          ID: /etc/foo.conf
    Function: file.managed
      Result: True
     Comment: File /etc/foo.conf exists with proper permissions. No changes made.
     Started: 14:01:46.765194
    Duration: 4.462 ms
     Changes:   

Summary for 3dedd8fe9f9f
------------
Succeeded: 1
Failed:    0
------------
Total states run:     1
Total run time:   4.462 ms
[root@master1 /]# salt 3dedd8fe9f9f state.apply foo_state pillar='{"test": ["a"]}'
3dedd8fe9f9f:
----------
          ID: /etc/foo.conf
    Function: file.managed
      Result: True
     Comment: File /etc/foo.conf exists with proper permissions. No changes made.
     Started: 14:02:09.330459
    Duration: 5.295 ms
     Changes:   

Summary for 3dedd8fe9f9f
------------
Succeeded: 1
Failed:    0
------------
Total states run:     1
Total run time:   5.295 ms
[root@master1 /]# salt 3dedd8fe9f9f state.apply foo_state pillar='{"test": ["a:b"]}'
3dedd8fe9f9f:
    Data failed to compile:
----------
    Rendering SLS 'base:foo_state' failed: found unexpected ':'
ERROR: Minions returned with non-zero exit code

Minion logs around the error:

2019-11-26 14:24:41,920 [salt.template    :120 ][DEBUG   ][2912] Rendered data from file: /var/cache/salt/minion/files/base/foo_state/init.sls:
#  Fail with state.apply w/ pillar='{"test": ["a:b"]}'
/etc/foo.conf:
  file.managed:
    - context:
        foo: [u'a:b']

2019-11-26 14:24:41,920 [salt.loaded.int.render.yaml:55  ][WARNING ][2912] Using the old YAML Loader for rendering, consider disabling this and using the tojson filter.
2019-11-26 14:24:41,920 [salt.state       :3487][CRITICAL][2912] Rendering SLS 'base:foo_state' failed: found unexpected ':'

Versions Report

[root@3dedd8fe9f9f /]# salt --versions-report
Salt Version:
           Salt: 2019.2.2
 
Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: Not Installed
      docker-py: Not Installed
          gitdb: Not Installed
      gitpython: Not Installed
          ioflo: Not Installed
         Jinja2: 2.7.2
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.5.6
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 2.7.5 (default, Aug  7 2019, 00:51:29)
   python-gnupg: Not Installed
         PyYAML: 3.11
          PyZMQ: 15.3.0
           RAET: Not Installed
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.2.1
            ZMQ: 4.1.4
 
System Versions:
           dist: centos 7.6.1810 Core
         locale: UTF-8
        machine: x86_64
        release: 5.0.0-35-generic
         system: Linux
        version: CentOS Linux 7.6.1810 Core

[sagetherage]

@oeuftete sorry about the stalebot, this should help and @garethgreenaway self-assigned now I need to find some time for him to work on it 😃

[oeuftete]

No longer reproducible in 3002.