Turn NOTE into docstring
Turn NOTE into docstring

conductor.base_manager._register_and_validate_hardware_interfaces had a
note at the top about what exceptions might be raised. Turn this into a
proper docstring.

Change-Id: I60b3e864f4cfba38ed7d12caf3bf723d73ab9e39
Partial-Bug: #1524745

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