2019.2 External file_tree pillar is broken with salt-ssh

Description of Issue

Having configured a file tree external pillar (without templating enabled), salt-ssh call results in the following trace:

[ERROR   ] TypeError encountered executing state.apply: Object of type bytes is not JSON serializable
Traceback (most recent call last):
  File "/Users/user1/Library/Python/3.7/lib/python/site-packages/salt/client/ssh/__init__.py", line 1159, in run_wfunc
    result = self.wfuncs[self.fun](*self.args, **self.kwargs)
  File "/Users/user1/Library/Python/3.7/lib/python/site-packages/salt/client/ssh/wrapper/state.py", line 513, in apply_
    return highstate(**kwargs)
  File "/Users/user1/Library/Python/3.7/lib/python/site-packages/salt/client/ssh/wrapper/state.py", line 705, in highstate
    roster_grains)
  File "/Users/user1/Library/Python/3.7/lib/python/site-packages/salt/client/ssh/state.py", line 193, in prep_trans_tar
    salt.utils.json.dump(pillar, fp_)
  File "/Users/user1/Library/Python/3.7/lib/python/site-packages/salt/utils/json.py", line 121, in dump
    return json_module.dump(obj, fp, **kwargs)  # future lint: blacklisted-function
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/__init__.py", line 179, in dump
    for chunk in iterable:
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/encoder.py", line 431, in _iterencode
    yield from _iterencode_dict(o, _current_indent_level)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/encoder.py", line 405, in _iterencode_dict
    yield from chunks
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/encoder.py", line 405, in _iterencode_dict
    yield from chunks
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/encoder.py", line 438, in _iterencode
    o = _default(o)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type bytes is not JSON serializable

This does not occur when using Python2.7.

Setup

Setup pillar.file_tree

ext_pillar:
  - file_tree:
        root_dir: file-tree
        follow_dir_links: False
        keep_newline: True

Place binary file in file_tree.

Steps to Reproduce Issue

Attempt to apply state using salt-ssh.

Versions Report

Salt Version:
           Salt: 2019.2.0

Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: 2.7.3
      docker-py: Not Installed
          gitdb: Not Installed
      gitpython: Not Installed
          ioflo: Not Installed
         Jinja2: 2.10.1
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: 1.0.12
   msgpack-pure: Not Installed
 msgpack-python: 0.6.1
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 3.7.3 (default, Mar 27 2019, 09:23:15)
   python-gnupg: Not Installed
         PyYAML: 3.13
          PyZMQ: 18.0.1
           RAET: Not Installed
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.3.1

System Versions:
           dist:
         locale: UTF-8
        machine: x86_64
        release: 18.6.0
         system: Darwin
        version: 10.14.5 x86_64

Start in salt/client/ssh/state.py at prep_trans_tar, where the pillar is written with salt.utils.json.dump, and review salt/utils/json.py. Reproduce the issue with a file_tree pillar containing a binary file and a salt-ssh state.apply call under Python 3. Done means the pillar can be transferred without the bytes-not-JSON-serializable error.