Now when user requests a list of artifacts glare returns
a json dict that has a section called after the type name,
which contains the list of the artifacts.
Example:
GET /artifacts/my_artifacts
{"my_artifacts": [...]}
It's not really a resful approach, so it's suggested to create a
unified section 'artifacts' for all cases, i.e. return
{"artifacts": [...]}
Change-Id: I2afb80fc7285bb8111a45a88d03f8ea21052f871
8348e98224