Tactical: Need better testing of the inheritance system

[sh8121att]

Need more fine grained unit testing of the inheritance system to ensure future model changes don't break it.
(HP = HostProfile, BN = BaremetalNode)

• Test that child HP can override simple parent HP attributes
• Test that child HP can set missing parent HP attributes
• Test that child HP can add members to simple list parent HP attributes (e.g. tags)
• Test that child HP can remove members from simple list parent HP attributes (e.g. tags)
• Test that child HP can add members to subpart list parent HP attributes (e.g. interfaces)
• Test that child HP can override subpart attributes from parent HP attributes (e.g. HostInterface attribute in interfaces list)
• Test that child HP can remove member from subpart list parent HP attributes (e.g. partition)