salt: [DOCS] cmd.run does not run as the user's default gid

Description of Issue

With salt 2018.3.4, using runas in a cmd.run would run the command with the uid and gid of the user account requested.

In 2019.2.0, it runs with the uid of the user account, but the gid is set to root.

Adding the kwarg group to the state resolves this - but this is not mentioned in the docs.

Setup

# cat > /etc/salt/minion.d/localminion.conf <<EOF
use_master_when_local: False
file_client: local
EOF

# mkdir -p /srv/salt
# cat > /srv/salt/test.sls <<EOF
runas salt:
  cmd.run:
    - name: id
    - runas: salt


runas salt with group:
  cmd.run:
    - name: id
    - runas: salt
    - group: salt
EOF

# useradd  -m -k /etc/skel -s /bin/bash salt

Steps to Reproduce Issue

# salt-call state.apply test
local:
----------
          ID: runas salt
    Function: cmd.run
        Name: id
      Result: True
     Comment: Command "id" run
     Started: 10:11:12.416785
    Duration: 53.337 ms
     Changes:
              ----------
              pid:
                  2082
              retcode:
                  0
              stderr:
              stdout:
                  uid=1009(salt) gid=0(root) groups=0(root),1010(salt) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
----------
          ID: runas salt with group
    Function: cmd.run
        Name: id
      Result: True
     Comment: Command "id" run
     Started: 10:11:12.470421
    Duration: 56.659 ms
     Changes:
              ----------
              pid:
                  2098
              retcode:
                  0
              stderr:
              stdout:
                  uid=1009(salt) gid=1010(salt) groups=1010(salt) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

Summary for local
------------
Succeeded: 2 (changed=2)
Failed:    0
------------
Total states run:     2
Total run time: 109.996 ms

Versions Report

# salt-call --versions-report
Salt Version:
           Salt: 2019.2.0

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, Jun 20 2019, 20:27:34)
   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: 3.10.0-957.27.2.el7.x86_64
         system: Linux
        version: CentOS Linux 7.6.1810 Core