Fix docstrings in conductor manager
Fix docstrings in conductor manager

Remove NodeCleaningFailure exception from docstrings of two methods,
they are not raise it.

Change-Id: I7885d359a613c9ef9f82953cfef67176f94ea59e

pshchelo/ironic,pshchelo/ironic,openstack/ironic,openstack/ironic,SauloAislan/ironic,SauloAislan/ironic