Use G_N_ELEMENTS() more

Use G_N_ELEMENTS() more

In a few places we still use the good old:

  sizeof(var) / sizeof(var[0])
  sizeof(var) / sizeof(int)

The G_N_ELEMENTS() macro is preferred though. In a few places we
don't link with glib, so provide the macro definition.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Kristina Hanicova <khanicov@redhat.com>