How to use DiskPartition?

[vikhari]

Issue ported from old casework github repo (issue 18).
Original author: casework

So DiskPartition has the following properties:

• mountPoint
• partitionID
• partitionLength
• partitionOffset
• spaceLeft
• spaceUsed
• totalSpace
• diskPartitionType
• createdTime

These properties seem to suggest that this property bundle should be placed in a Trace.
However, in plaso's use case, it needs to be placed in a Relationship object and only use a subset of these properties
(image -> partOffset = 4 -> the partition)
Should we create two separate property bundles like we did with File and PathRelation?