Storage Policy / DiskFile Interface Support

The EC branch currently has minimal DiskFile support (one API) and
a big todo item for the rest.  This patch completes the support as
well as addresses a change to the one existing interface where we
used to pass the object directory name into DiskFile but have now
decided to pass in the policy index instead and let DiskFile build
the object directory name.  This patch includes:

- change interface param from directory name to policy index
- replace DiskFile DATADIR with Diskfile module method to
  return object directory name based on index (in all
  DiskFile and test files)
- do the same for ASYNCDIR, although not required, might
  be nice for debug/organization to have the async updates
  in per policy directories
- removal of object dir notion from StoragePoicy object

The patch also includes 2 updates unrelated to diskfile that were
suggested during review:
1) avoid use of extra parm in obj server HTTP verb handlers
2) modify storage_policy module to remove test code policy
defaults and update related test code to provide them

Still a few todo items labeled XXX (todo in a different patch later):
- had to do some of the updater policy work to get things
  to function but supporting policies for the updater
  is a separate activity
- same kind of thing with ssync, had to hack in one minor
  thing to get things to work but a different activity
  will be entered on Trello for ssync policy support

Change-Id: I71eab0788325f715b2787e818d41dc3fa58a7046
Implements: blueprint storage-policies