generic approach to mock tests so assertions can be shared

 - fixing up client
 - removed unecessary schema model
 - cherry-picked duplicate changes
 - add rotating responses
 - continued with mock test strategy
 - move metatests to root folder

Change-Id: I1b484e3959fbea5b7e3643fd2831f44ba82e9b1c
fixing images v2.0 model/client to make tests pass

Needed by
Change-Id: Ia889aec302f2f43d3a1ffbb1b63ad59b85fc4133

 - rebased with dependency
 - using explicit mapping and _remove_empty_values to create model dict
   now
 - implement sotring of raw image data
 - fixing serialization of image model
 - cherry-picked from a fast-forward commit

Change-Id: Ifb0f895a2d9d18bad6e912c9b446394c1a94ad73
Merge "generic approach to mock tests so assertions can be shared"
Merge "fixing images v2.0 model/client to make tests pass"