Comment 13 for bug 1781991

Xenial verification

First, reproducing the bug with the current package:
ubuntu@xenial-berification-sssd-sudo:~$ apt-cache policy libsss-sudo
libsss-sudo:
  Installed: (none)
  Candidate: 1.13.4-1ubuntu1.14
  Version table:
     1.13.4-1ubuntu1.14 500
        500 http://br.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages

ubuntu@xenial-berification-sssd-sudo:~$ sudo apt install libsss-sudo
...
ubuntu@xenial-berification-sssd-sudo:~$ grep ^sudoers /etc/nsswitch.conf
sudoers: files sss

Removing sss:
ubuntu@xenial-berification-sssd-sudo:~$ sudo vi /etc/nsswitch.conf
ubuntu@xenial-berification-sssd-sudo:~$ grep ^sudoers /etc/nsswitch.conf
sudoers: files

Reinstall puts it back:
ubuntu@xenial-berification-sssd-sudo:~$ sudo apt install --reinstall libsss-sudo
...
ubuntu@xenial-berification-sssd-sudo:~$ grep ^sudoers /etc/nsswitch.conf
sudoers: files sss

Now enabling proposed:
ubuntu@xenial-berification-sssd-sudo:~$ apt-cache policy libsss-sudo
libsss-sudo:
  Installed: 1.13.4-1ubuntu1.14
  Candidate: 1.13.4-1ubuntu1.15
  Version table:
     1.13.4-1ubuntu1.15 500
        500 http://br.archive.ubuntu.com/ubuntu xenial-proposed/main amd64 Packages
 *** 1.13.4-1ubuntu1.14 500
        500 http://br.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages

Removing sss again from nsswitch.conf:
ubuntu@xenial-berification-sssd-sudo:~$ sudo vi /etc/nsswitch.conf
ubuntu@xenial-berification-sssd-sudo:~$ grep ^sudoers /etc/nsswitch.conf
sudoers: files

Doing the upgrade this time doesn't add sss back:
ubuntu@xenial-berification-sssd-sudo:~$ sudo apt install libsss-sudo
Reading package lists... Done
...
ubuntu@xenial-berification-sssd-sudo:~$ grep ^sudoers /etc/nsswitch.conf
sudoers: files

And I have the new package installed now:
ubuntu@xenial-berification-sssd-sudo:~$ apt-cache policy libsss-sudo
libsss-sudo:
  Installed: 1.13.4-1ubuntu1.15
  Candidate: 1.13.4-1ubuntu1.15
  Version table:
 *** 1.13.4-1ubuntu1.15 500
        500 http://br.archive.ubuntu.com/ubuntu xenial-proposed/main amd64 Packages

A fresh install, though, adds sss back, as expected:
ubuntu@xenial-berification-sssd-sudo:~$ sudo apt purge libsss-sudo
Reading package lists... Done
Building dependency tree
...
ubuntu@xenial-berification-sssd-sudo:~$ grep ^sudoers /etc/nsswitch.conf
ubuntu@xenial-berification-sssd-sudo:~$
ubuntu@xenial-berification-sssd-sudo:~$ sudo apt install libsss-sudo
Reading package lists... Done
...
ubuntu@xenial-berification-sssd-sudo:~$ grep ^sudoers /etc/nsswitch.conf
sudoers: files sss

Xenial verification succeeded.