This addresses a long-standing TODO in the BlobStatter interface to
clean it up. Just like all new Go programmers, I misused channels in
APIs. I should've cleaned this up years ago.
While here, I also added a context.
The rest should get contexts later.
This also cleans up a few things here & there.
The pkg/client statting no longer does batching, which added a lot of
complexity. There was a comment saying something like "once we have
SPDY, we can delete this". Well, we have HTTP/2 now, so seems
deletable.
All tests pass.
Change-Id: I034ce07d9b70e5cc9e5482213368993e638d4bc8
0e8980b54b