When an item is added to an array, then the array is realloc()ed (to size+1),

When an item is added to an array, then the array is realloc()ed (to size+1),
and the item is copied (strdup()) to the array.
Thus, when an item is removed from an array, memory allocated for that item
should be freed, successive items should be left-shifted and the array
realloc()ed again (size-1).

Additional changes:
- If strdup() fails in add_to_array(), then an array should be
  realloc()ed again to original size.
- Initialize an array in list_all_containers().

Signed-off-by: Tomasz Blaszczak <tomasz.blaszczak@consult.red>