Code review comment for lp:~wallyworld/juju-core/merge-new-image-metadata

Reviewers: mp+190898_code.launchpad.net,

Message:
Please take a look.

Description:
Merge new image metadata with existing

When image id metadata is generated, any existing metadata is
now loaded and then the new metadata is merged in. This allows
the generate-image plugin to be run multiple times to build up
metadata for multiple images. Some fairly extensive refactoring
to how image metadata search constraints are set up was required.

https://code.launchpad.net/~wallyworld/juju-core/merge-new-image-metadata/+merge/190898

(do not edit description out of merge proposal)

Please review this at https://codereview.appspot.com/14663043/

Affected files (+843, -367 lines):
   A [revision details]
   M cmd/plugins/juju-metadata/imagemetadata.go
   M cmd/plugins/juju-metadata/imagemetadata_test.go
   M cmd/plugins/juju-metadata/validateimagemetadata_test.go
   M environs/imagemetadata/generate.go
   A environs/imagemetadata/generate_test.go
   A environs/imagemetadata/marshal.go
   A environs/imagemetadata/marshal_test.go
   M environs/imagemetadata/simplestreams.go
   M environs/imagemetadata/simplestreams_test.go
   A environs/imagemetadata/testing/testing.go
   M environs/imagemetadata/validation_test.go
   M environs/simplestreams/simplestreams.go
   M environs/tools/marshal.go