[BUG][V3005] Pillar-root doesnt work

Description
Related issue: https://github.com/saltstack/salt/issues/16873

The --pillar-root option doesn't work. Salt is always sourcing the standard pillar-root

Setup

Please be as specific as possible and give set-up details.

• on-prem machine
• VM (Virtualbox, KVM, etc. please specify)
• VM running on a cloud service, please be explicit and add details
• container (Kubernetes, Docker, containerd, etc. please specify)
• or a combination, please be explicit
• jails if it is FreeBSD
• classic packaging
• onedir packaging
• used bootstrap to install

Steps to Reproduce the behavior
create a pillar test in /srv/salt/pillar/config.sls but not in another pillar-root :

(cluster)-[xxxx@admin ~]$ grep -A1 toto: /srv/salt/pillar/config.sls
toto:
  tutu: test
(cluster)-[xxxx@admin ~]$ grep -A1 toto: /opt/another_salt_pillar_dir/config.sls
(cluster)-[xxxx@admin ~]$

Expected behavior
Run:
This is normal:

(cluster)-[xxxx@admin1 ~] $ salt-call pillar.get  toto
local:
    ----------
    tutu:
        test

This is not normal and should be return nothing:

(cluster)-[xxxx@admin1 ~] $ salt-call --pillar-root=/opt/another_salt_pillar_dir/ pillar.get  toto
local:
    ----------
    tutu:
        test

Versions Report

Salt Version:
          Salt: 3005
 
Dependency Versions:
          cffi: 1.9.1
      cherrypy: Not Installed
      dateutil: Not Installed
     docker-py: Not Installed
         gitdb: Not Installed
     gitpython: Not Installed
        Jinja2: 2.11.1
       libgit2: Not Installed
      M2Crypto: 0.35.2
          Mako: Not Installed
       msgpack: 0.6.2
  msgpack-pure: Not Installed
  mysql-python: Not Installed
     pycparser: Not Installed
      pycrypto: Not Installed
  pycryptodome: Not Installed
        pygit2: Not Installed
        Python: 3.6.8 (default, Nov 16 2020, 16:55:22)
  python-gnupg: Not Installed
        PyYAML: 3.13
         PyZMQ: 18.0.1
         smmap: Not Installed
       timelib: Not Installed
       Tornado: 4.5.3
           ZMQ: 4.1.4
 
System Versions:
          dist: centos 7 Core
        locale: UTF-8
       machine: x86_64
       release: 3.10.0-1160.76.1.el7.x86_64
        system: Linux
       version: CentOS Linux 7 Core
 

Additional context
Nothing to Add

Start with the salt-call command path for the --pillar-root option and compare its pillar lookup with the paths shown in the reproduction. Use /srv/salt/pillar/config.sls and /opt/another_salt_pillar_dir/config.sls to verify which source is read. Done means salt-call --pillar-root=/opt/another_salt_pillar_dir/ pillar.get toto does not return the value from the standard pillar root.