Skip non-base properties in patch method

It's currently impossible to update properties which are defined in
image schema and which are not a base image property. Proposed fix skips
every non-base property when building a json patch, that is used to
update image properties through glance API.

Change-Id: I3b35cef379fcf437715e2966f9a0d25c1b4e4016
Closes-Bug: #1371559
Merge "Skip non-base properties in patch method"