This change updates the storagenode piecestore apis to expose access to
the full piece size stored on disk. Previously we only had access to
(and only kept a cache of) the content size used for all pieces. This
was inaccurate when reporting the amount of disk space used by nodes.
We now have access to the total content size, as well as the total disk
usage, of all pieces. The pieces cache also keeps a cache of the total
piece size along with the content size.
Change-Id: I4fffe7e1257e04c46021a2e37c5adc6fe69bee55
14fd6a9ef0