Tighten up conditions for shrinking shards to their root container so
that *all* shard ranges must be included in the single compactible
sequence. Previously shard ranges in states that were not eligible for
shrinking (such as CREATED) would not prevent other shards shrinking
to root.
Change-Id: I3da9b59f6744b10853d89b51ae15f05bdd51d02d