Assume ETag is always in the metadata

Currently the GET and HEAD calls always assume that the ETag is
present in the on-disk metadata, as they index the metadata dictionary
directly for the value to fill in the proper response header (a
KeyError would be thrown if missing and turn into a 503).

The close code that handles quarantining checked to see if an ETag is
present in the metadata before making the comparison. However, a close
operation would never even be attempted if an ETag was not present,
since the response headers are filled in before the object is read.

Change-Id: I5032251414eceb38079d235504cc9e589dea5f3e
Signed-off-by: Peter Portante <peter.portante@redhat.com>
Split backends off swift/common/db.py

The main purpose of this patch is to lay the groundwork for allowing
the container and account servers to optionally use pluggable backend
implementations. The backend.py files will eventually be the module
where the backend APIs are defined via docstrings of this reference
implementation. The swift/common/db.py module will remain an internal
module used by the reference implementation.

We have a raft of changes to docstrings staged for later, but this
patch takes care to relocate ContainerBroker and AccountBroker into
their new home intact.

Change-Id: Ibab5c7605860ab768c8aa5a3161a705705689b04
Merge "Split backends off swift/common/db.py"
Improve unittest coverage of account reaper

Add more unittests for account_reaper in order to
improve code coverage.

Fixes: bug #1210045
Change-Id: I73490f80ac70b814a0abc490dc932f2a86fca703
Man page lintian errors and warnings

Used groff to recreate the errors. I believe all the issues
except `binary-without-manpage` are solved. Would like
confirmation from someone using Lintian.

Closes-Bug: #1210114
Change-Id: I533205c53efdb7cdf3645cc3e3dc487f9ee5640a
Merge "Man page lintian errors and warnings"