feat: List blocks under blockstorage endpoint

- Supports limits and markers

- The way swift and disk storage drivers handle this are a bit different
  disk returns an empty list on a bad marker
  but swift handles this differently,
  for eg: if the contents of the container are [a,b,c,x,y,z]
  marker='p' returns [x,y,z] based on alphabetical ordering.
  Therefore, swift has been mocked accordingly.
Merge remote-tracking branch 'upstream/master' into list_blockstorage_endpoint

Conflicts:
	deuce/transport/wsgi/v1_0/blockstorage.py
bugfix: contents needs to be decoded

the contents returned from swift are in bytes and need
to be decoded.

Also includes changed tests to verify this.
claenup: removed comments
fix: test_blockstorage

Add test for no markers, and use one of the returned storageids
as a marker for testing with markers
Merge remote-tracking branch 'upstream/master' into list_blockstorage_endpoint

Conflicts:
	deuce/model/blockstorage.py
fix: conflicts resolution

removed 501 from wsgi.errors as we not using it anymore
fix: Add header for json response, instead of query string
Merge pull request #192 from TheSriram/list_blockstorage_endpoint

feat: List blocks under blockstorage endpoint