su command's return value is wrong when pam_sss is enabled.

Issue

When a command is run via su from root, the exit status is always 0, even if the command fails.

For example:

# service sssd status
sssd (pid  3009) is running...

# su - local_user -c "ls -8" ; echo $?
ls: invalid option -- '8'
Try `ls --help' for more information.
0

# service sssd stop
Stopping sssd:                                             [  OK  ]
# su - local_user -c "ls -8" ; echo $?
ls: invalid option -- '8'
Try `ls --help' for more information.
2

• User local_user is a local user (from /etc/passwd file).
• If we stop the sssd service(or remove pam_sss from the PAM session section, then the command's exit status is correct.