This adds support to the glance client library for removing
properties from an image. Properties to be removed must be
explicitly listed. There is no equivalent of the 'purge_props'
functionality in v1.
Also beefed up testing around create since some of the
functionality is the same as update.
Fixes bug 1206472
Change-Id: I16f4c39cdfc8a0cd07bede600461b7a289fbb080