recovery: added 'recovery_speed' and 'iteration_speed' to statistics. Both values are mesuared in records per second.
iteration: added new iteration flag: DNET_IFLAGS_NO_META which turns off reading extended header from blob and speedups iteration, but all keys that will be returned by such iteration will have empty metadata (timestamp and user_flags).
recovery: added '-M' option to dnet_recovery which speedups iteration phases of recovery but sacrifices checking metadata. Recovery with this option will not check metadata, will not replace old records by new ones and will only copy some available replica of keys to groups which do not have these keys.
pytests: updated some test cases of test_recovery to use new '-M' option
pytests: added case to test_session_iterator that check iterating with no_meta flag
iteration: removed double checking of ranges - keys is already filtered in eblob.