Remove unused return value from take_action

This commit removes return values from take_action(). Because they are
unused in cliff[1] and to prevent developers misunderstanding.

[1]
http://git.openstack.org/cgit/openstack/cliff/tree/cliff/command.py#n55

Change-Id: I1a81e163acae17005f49decb8cb7ffee52944d26
5 files changed