fix memory leaks in invocations of PyObject_Call

fix memory leaks in invocations of PyObject_Call

- Various functions in the Python bindings have expressions of the form:

  PyObject_Call(callable,
                  Py_BuildValue(fmtstring, ...), NULL);

  This leaks memory for the case when Py_BuildValue succeeds (it returns a
  new reference, which is never freed; PyObject_Call doesn't steal the
  reference): the argument tuple and all of its components will not be
  freed (until the process exits).

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