Description of problem:

  The new samba_krb5_wrapper that allows CUPS to use Kerberos to
  authenticate with printers doesn't list SMB devices when called with
  no arguments.  As a result, the SMB protocol isn't listed as a 
  possible printer connection mechanism.

Version-Release number of selected component (if applicable):

  samba-4.4.4-9

How reproducible:

  100%

Steps to Reproduce:

  run "lpinfo -v"

  or

  run "/usr/lib/cups/backend/smb"

Actual results:

  # lpinfo -v
  serial serial:/dev/ttyS0?baud=115200
  network ipps
  network lpd
  network socket
  network https
  network http
  network ipp

  # /usr/lib/cups/backend/smb
  DEBUG: SMBSPOOL_KRB5 - Started with uid=0

  DEBUG: SMBSPOOL_KRB5 - AUTH_INFO_REQUIRED is not set
  ATTR: auth-info-required=negotiate

Expected results:

  # lpinfo -v
  serial serial:/dev/ttyS0?baud=115200
  network ipps
  network lpd
  network socket
  network https
  network http
  network ipp
  network smb

  (Last entry "network smb" should be included)

  # /usr/lib/cups/backend/smb 
  network smb "Unknown" "Windows Printer via SAMBA"

Additional info:

  When the "lpinfo -v" command is used, cupsd calls
  /usr/lib/cups/daemon/cups-deviced to execute all the backends in
  /usr/lib/cups/backend with no arguments.  When a backend is called
  with no arguments, it should list all the devices that are accessible
  via that backend.

  This mechanism is also used by the Web UI and system-config-printer to
  enumerate  possible  print  devices.   If  samba_krb5_wrapper  doesn't
  provide the proper out put, SMB will not be listed as an option in the
  GUI when installing new printers.