Add X-Backend-Timestamp on more object server responses

It's particularly interesting on writes (PUT, POST, DELETE) where the
current on-disk timestamp would prevent the object server from serving
the incoming request and returns 409 Conflict.

The FakeConn has also been updated to respond in kind for 409's on
expect and all responses generaly just cause it's good to keep fakes in
line with the reals - not that I expected any existing tests to break
because of the new headers.

Change-Id: Iac6fbd2f872a9521bb2db84a333365b69f54fb6c
Put proxy-logging in object expirer's sample config

It's generally better to have logs for something than to not have
logs. This way, the object expirer (if using the sample config as a
starting point) will log what it does.

Note that the container reconciler's sample config already contains
proxy-logging, as does the proxy server's. The object expirer is the
odd man out.

Change-Id: I32aac99131746501820319b94405440c1934a694
Enable object system metadata on PUTs

This patch takes a first step towards support
for object system metadata by enabling headers
in the x-object-sysmeta- namespace to be
persisted when objects are PUT. This should be
useful for other pending patches such as on
demand migration and server side encryption
(https://review.openstack.org/#/c/64430/ and
https://review.openstack.org/#/c/76578/1).

The x-object-sysmeta- namespace is already
reserved/protected by the gatekeeper and
passed through the proxy. This patch modifies
the object server to persist these headers
alongside user metadata when an object is
PUT.

This patch will preserve existing object
system metadata and ignore any new system
metadata when handling object POSTs,
including POST-as-copy operations. Support
for modification of object system metadata
with a POST request requires further work
as discussed in the blueprint.

This patch will preserve existing object
system metadata and update it with new
system metadata when copying an object.

A new probe test is added which makes use of
the BrainSplitter class that has been moved
from test_container_merge_policy_index.py to
a new module brain.py.

blueprint object-system-metadata

Change-Id: If716bc15730b7322266ebff4ab8dd31e78e4b962
fix expirer bug with unicode container listings

If the container names in the expirer's account are returned as
unicode strings (as is the case with some json libraries), the
expirer compared eg u'1' == '1', which is problematic. This patch
ensures that the unicode is coerced to ascii so the comparison
is correct.

Change-Id: I72b322e7513f7da32e8dc75c6bf0e7e016948c88
Merge "Enable object system metadata on PUTs"
Merge "fix expirer bug with unicode container listings"
Merge "Add X-Backend-Timestamp on more object server responses"
Merge "Put proxy-logging in object expirer's sample config"