Add optional locking to swift-ring-builder

If invoked as 'swift-ring-builder-safe' the directory containing the builder
file provided will be locked (via lock_parent_directory()). This provides a
small safe guard against multiple instances of the swift-ring-builder (or
other utilities that observe this lock) from attempting to write to or read
the builder/ring files while operations are in progress.

This is particularly useful in environments where ring management has been
automated (via Chef or custom solutions) but the operator still occasionally
needs to manually interact with the ring.

DocImpact

Change-Id: Ia362744a8151a91bfb586d01da582906726852e6
Handle access_log_headers in proxy_logging

 * in etc/proxy-server.conf-sample, there is an access_log_headers directive in proxy_logging middleware.
   but current code doesn't handle it. This patch enables proxy_logging to handle access_log_headers.

Change-Id: I03337ccc4f48625af3f578ed543da992d3eec2bd
Merge "Handle access_log_headers in proxy_logging"