handle errors when constructing lists in the Python bindings

handle errors when constructing lists in the Python bindings

- Various functions in the Python bindings construct lists of objects, but
  assume that all calls succeed. Each of these could segfault under
  low-memory conditions: if the PyList_New() call fails,
  PyList_Append(NULL, item ) will segfault. Similarly, although
  Py_List_Append(list, NULL) is safe, Py_DECREF(NULL) will segfault.

Signed-off-by: Ales Kozumplik <akozumpl@redhat.com>