Meta server: display total chunk server count if no storage tiers available.
Qfs client lib: add optional min and max tiers fields to change replication rpc.
Meta server: set replication op fix show() method, consider set replication with less than 0 replication factor and defined min or max tiers valid. Do not change replication in such case, only change storage tiers.
Meta server: do not emit change replication log entry if replication and storage tiers did not change.
Meta server: fix backward compatibility with previous chunk server versions with no storage tiers.
Meta server: allow to perform non hierarchical chunk placement with write append. Setting meta server parameter metaServer.appenPlacementIgnoreMasterSlave to 1 enabled this mode.
Merge branch 'topic/disk_buffer_manager' into topic/net_io_threads