Ensure V-38574 works reliably on CentOS

This patch ensures that the tasks can find the right PAM
files to do the checks for V-38574. CentOS systems usually
symlink password-auth to password-auth-ac, but this symlink
is missing in the gate image.

The tasks now look for the password-auth file and this will work
properly on a generic CentOS 7 system as well as within the gate image.

Change-Id: I24281530df8bc939a823ffcc6187882574d266f6

tox.ini

@@ -105,16 +105,13 @@ commands =
 # NOTE(odyssey4me): We have to skip V-38462 as openstack-infra are now building
 #                   images with apt config Apt::Get::AllowUnauthenticated set
 #                   to true.
-# NOTE(mhayden):    V-38574: OpenStack infra images have non-standard pam
-#                   configurations that don't match a standard CentOS 7 server
-#                   or cloud image. It must be skipped.
 commands =
     rm -rf {homedir}/.ansible
     git clone https://git.openstack.org/openstack/openstack-ansible-plugins \
               {homedir}/.ansible/plugins
     ansible-playbook -i {toxinidir}/tests/inventory \
                      -e "rolename={toxinidir}" \
-                     --skip-tag V-38462,V-38574 \
+                     --skip-tag V-38462 \
                      {toxinidir}/tests/test.yml
 
 

vars/redhat.yml

@@ -15,7 +15,7 @@
 
 # Configuration file paths
 pam_auth_file: /etc/pam.d/system-auth
-pam_password_file: /etc/pam.d/password-auth-ac
+pam_password_file: /etc/pam.d/password-auth
 vsftpd_conf_file: /etc/vsftpd/vsftpd.conf
 
 # Package names