lxc init fails on Python 3

Description of Issue/Question

lxc.init fails with:

Passed invalid arguments to lxc.init: a bytes-like object is required, not 'str'

First I was not sure if this is a bug, but then I found issue #46299 , and symptoms seem to be similar and lxc.create works fine. See below.

Setup

Cloud provider with lxc driver and profiles for salt cloud (config) and lxc (pillar).

This works:

# salt myminion lxc.create container2 profile=alpine
myminion:
    ----------
    result:
        True
    state:
        ----------
        new:
            stopped
        old:
            None

But this does not:

# salt myminion lxc.init container3 profile=alpine
myminion:
    Passed invalid arguments to lxc.init: a bytes-like object is required, not 'str'
    
        Initialize a new container.
    
        This is a partial idempotent function as if it is already provisioned, we
        will reset a bit the lxc configuration file but much of the hard work will
        be escaped as markers will prevent re-execution of harmful tasks.
[.... whole docstring ....]
        
ERROR: Minions returned with non-zero exit code

Steps to Reproduce Issue

• Install salt from the py3 repo on Ubuntu 18.04 (bionic)
• Run the lxc.init module.

Versions Report

# salt-call --versions-report
Salt Version:
           Salt: 2019.2.0
 
Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: 2.6.1
      docker-py: Not Installed
          gitdb: 2.0.3
      gitpython: 2.1.8
          ioflo: Not Installed
         Jinja2: 2.10
        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: 3.6.7 (default, Oct 22 2018, 11:32:17)
   python-gnupg: 0.4.1
         PyYAML: 3.12
          PyZMQ: 16.0.2
           RAET: Not Installed
          smmap: 2.0.3
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.2.5
 
System Versions:
           dist: Ubuntu 18.04 bionic
         locale: UTF-8
        machine: x86_64
        release: 4.15.0-46-generic
         system: Linux
        version: Ubuntu 18.04 bionic

Start with the lxc.init entry point and compare its argument handling with lxc.create, then reproduce the failure using Python 3 on Ubuntu 18.04 as described. Done means lxc.init completes without the bytes-like-object error and initializes the container successfully.