In order that something consuming an artifact can have access to extra
builder specific data add the State method which allows the caller to
ask for arbitary values by name.
This commit adds support for a post-processor that produces a compressed
archive that can be uploaded to an OpenStack cluster through either
the Horizon web interface or Glance.
Vasiliy Tolstov
Chris Bednarski
Julian Phillips
Mitchell Hashimoto
John Bellone