samba: step 28 doesn't work without joining a domain

The whole setup essentially mimics "sudo apt install samba winbind".

By step 28, the user is asked to run "net usersidlist", but that command doesn't work anymore unless the machine is joined to a domain. Similarly, "wbinfo -u" won't list users.

I suggest to change step 28 into this:
"""
28. Verify winbind is alive:

  wbinfo -p

  has to return the text "Ping to winbindd succeeded" when run as a user or root

29. Verify winbind basic functionality:

  $ wbinfo --all-domains

  has to return two lines: one with "BUILTIN", the other with the unqualified hostname in all capitals. For example, a hostname like "trusty-samba-usersidlist" would be in the wbinfo output as "TRUSTY-SAMBA-USERSIDLIST".
"""

And remote the original step 29 with the note about providing a user to the pam stack.