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
00dbad0825