Add a resource type for baremetal node interfaces.
Rework BMNodeManager.create() to take individual arguments so it is
easier to test.
Improve method docs
Fix up some methods to behave more sensibly

Change-Id: If511df12d4e7eb404bd1aabd39d21d476bcb5d5c
Add tests for baremetal

Change-Id: I2aa2fd9c2614006a14fa37dcee5a8e68531a104c