[BUG] groups with duplicate GIDs are not returned by get_group_list

[nicholasmhughes]

Description

The following error is thrown when attempting to enforce optional group membership for a group which does not have a unique GID.

[ERROR   ] These values could not be changed: {'groups': ['adm', 'audio', 'cdrom', 'dialout', 'dip', 'floppy', 'netdev', 'plugdev', 'sudo', 'user', 'users', 'video']}
local:
----------
          ID: groups_manage_user
    Function: user.present
        Name: debian
      Result: False
     Comment: These values could not be changed: {'groups': ['adm', 'audio', 'cdrom', 'dialout', 'dip', 'floppy', 'netdev', 'plugdev', 'sudo', 'user', 'users', 'video']}
     Started: 14:57:44.820074
    Duration: 39.273 ms
     Changes:   

Summary for local
------------
Succeeded: 0
Failed:    1
------------
Total states run:     1
Total run time:  39.273 ms

Setup

Example state file:

# /srv/salt/groups.sls

manage_user:
  user.present:
    - name: debian
    - optional_groups: [user]

Steps to Reproduce the behavior

Add the user group with a duplicate GID, such as copying the users group line in /etc/group and then run the state.

salt-call state.apply groups

Running in TRACE log level points toward the problem:

TRACE   ] Trying os.getgrouplist for 'debian'
[TRACE   ] Group list for user 'debian': ['adm', 'audio', 'cdrom', 'debian', 'dialout', 'dip', 'floppy', 'netdev', 'plugdev', 'sudo', 'users', 'video']

The group listing is derived from GIDs, so the user group is not shown.

Expected behavior
While not the best practice, duplicate GIDs are a valid configuration which might be experienced on systems. The function should be able to list unique group names which might have duplicate GIDs.

Versions Report

salt --versions-report

(Provided by running salt --versions-report. Please also mention any differences in master/minion versions.)

Salt Version:
          Salt: 3005+0na.b18281e
 
Dependency Versions:
          cffi: Not Installed
      cherrypy: Not Installed
      dateutil: Not Installed
     docker-py: Not Installed
         gitdb: Not Installed
     gitpython: Not Installed
        Jinja2: 3.1.2
       libgit2: Not Installed
      M2Crypto: Not Installed
          Mako: Not Installed
       msgpack: 1.0.3
  msgpack-pure: Not Installed
  mysql-python: Not Installed
     pycparser: Not Installed
      pycrypto: 2.6.1
  pycryptodome: 3.14.1
        pygit2: Not Installed
        Python: 3.7.3 (default, Jan 22 2021, 20:04:44)
  python-gnupg: Not Installed
        PyYAML: 6.0
         PyZMQ: 23.0.0
         smmap: Not Installed
       timelib: Not Installed
       Tornado: 4.5.3
           ZMQ: 4.3.4
 
System Versions:
          dist: debian 10 buster
        locale: UTF-8
       machine: x86_64
       release: 4.19.0-21-amd64
        system: Linux
       version: Debian GNU/Linux 10 buster