Qfs client: allow to specify storage tiers with "S" file create parameters specification.
Meta server: fix rack storage tiers update; fix rack binary search -- do not assume that dummy argument is always on the right side; fix incorrect argument order in GetRackId(). Add storage tiers information to the PING response.
Layout emulator: update to compile.
Qfs common: minor optimization with empty host prefixes.
Qfs test: set rack ids in chunk server configuration files to be equal to the chunk servers' listen port number to put the two chunk servers into different "racks".