Refactor image model for glance v2

*Refactored image model to reflect changes in tests
*Changed ImagePatch class to ImageUpdate to give better context
*Refactored ImageUpdate and Member to reflect changes in tests
*Updated summary documentation and formatting to be consistent throughout
*Replaced id variable with id_
*Replaced file variable with file_

Change-Id: I57b50c369e36d86b6375ef1ecdc56b302d7f0644
Merge "Refactor image model for glance v2"