Meta server: pass storage tier range to the chunk servers by adding the corresponding fields to chunk allocation and replication RPCs; optimize chunk placement code to skip empty / non existent tiers; implement space and io accounting for chunk allocation and replications in flight; take into the account storage tiers in re-balancing and re-balance plan execution. Add "signed char" integer parser specialization to ValueParserT to ensure proper handling of int8_t used to pass storage tier information.