In order to get a better name, let's use oslo_utils reflection to
get function name in RetryDecorator call.
for example:
from oslo_utils import reflection
class Foo(object):
def test_fun(self):
pass
foo = Foo()
print(foo.test_fun.__name__) # "test_fun"
print(reflection.get_callable_name(foo.test_fun)) # "__main__.Foo.test_fun"
Change-Id: Ia7970b564e33ef7eafcd31fd907f4d53db1672f0