Run tests/unit/test_funcutils.py in PY3 enviroment

Fixed `func_closure` usage in openstack.common.funcutils module
and `func_code` usage in tests/unit/test_funcutils.py file.

Related to blueprint make-python3-compatible

Change-Id: I68d206c5fdb4143c7618449b83d102145e6ba54e
Merge "Run tests/unit/test_funcutils.py in PY3 enviroment"