user.present fails to both change primary group, and set old primary group as an additional group in same run

[terminalmage]

Description of Issue

When you change the default group of a user, but put their old default group into the groups list, the _changes() helper function in salt/states/user.py that determines what needs to be modified does not catch that the user's old default group will need to be added back. Because of this, that change is not made, causing the state to fail reporting that it couldn't properly set the groups. It must then be run a second time to add that group for the user.

Setup

I've put this into a Docker container for easy inspection and reproducibility. Run these Docker commands from the root of a git checkout of Salt.

NOTE: I've edited out a traceback that currently appears when you run this from the head of the master branch. I've reported that separately here.

% docker run --rm -it -v $PWD:/testing terminalmage/issues:56061 tail -n2 /etc/group
oldprimary:x:223344:
foo:x:112233:
% docker run --rm -it -v $PWD:/testing terminalmage/issues:56061 tail -n1 /etc/passwd
foo:x:112233:223344::/home/foo:/bin/bash
% docker run --rm -it -v $PWD:/testing terminalmage/issues:56061 cat /srv/salt/users.sls
foo:
  user.present:
    - uid: 112233
    - gid: 112233
    - allow_gid_change: True
    - groups:
      - oldprimary

Steps to Reproduce Issue

% docker run --rm -it -v $PWD:/testing terminalmage/issues:56061 salt-call state.apply
[ERROR   ] {u'gid': 112233, u'groups': ['foo']}
local:
----------
          ID: foo
    Function: user.present
      Result: False
     Comment: These values could not be changed: {u'groups': [u'oldprimary']}
     Started: 22:46:26.497176
    Duration: 1441.022 ms
     Changes:
              ----------
              gid:
                  112233
              groups:
                  - foo

Summary for local
------------
Succeeded: 0 (changed=1)
Failed:    1
------------
Total states run:     1
Total run time:   1.441 s

Versions Report

Salt Version:
           Salt: 3000

Dependency Versions:
           cffi: 1.12.2
       cherrypy: 17.3.0
       dateutil: 2.8.0
      docker-py: 3.7.2
          gitdb: 2.0.5
      gitpython: 2.1.11
         Jinja2: 2.10.1
        libgit2: 0.28.2
       M2Crypto: Not Installed
           Mako: 1.1.0
   msgpack-pure: Not Installed
 msgpack-python: 0.5.6
   mysql-python: Not Installed
      pycparser: 2.19
       pycrypto: 3.8.1
   pycryptodome: Not Installed
         pygit2: 0.28.2
         Python: 2.7.5 (default, Jun 20 2019, 20:27:34)
   python-gnupg: 0.4.4
         PyYAML: 5.1.2
          PyZMQ: 18.0.1
          smmap: 2.0.5
        timelib: 0.2.4
        Tornado: 4.5.3
            ZMQ: 4.3.1

System Versions:
           dist: centos 7.6.1810 Core
         locale: UTF-8
        machine: x86_64
        release: 5.4.15-arch1-1
         system: Linux
        version: CentOS Linux 7.6.1810 Core