test: make Fetcher use a RWMutex so fetch doesn't deadlock during enumerate

Change-Id: Iac1f18725231a298c2c636875647c3e6f3f081a4
Add pkg/blobserver/archiver for making Glacier archives.

From the package docs:

  Package archiver zips lots of little blobs into bigger zip files
  and stores them somewhere. While generic, it was designed to
  incrementally create Amazon Glacier archives from many little
  blobs, rather than creating millions of Glacier archives.

Change-Id: If304b2d4bf144bfab073c61c148bb34fa0be2f2d
Add integration test for websocket query

Change-Id: I37c48d5749c7bf31aa118b2bee0861aeb07c5ff3