Fixes for sb_rand and sb_memory and supported parameters extension for memory test

[evvoevod]

First commit fixes critical bug in sb_rand which broke Gaussian distribution due to 'rand_iter' initialized to zero after Special distribution has got dropped. Second commit extends supported --memory-total-size and --memory-block-size parameters values allowing total size to be smaller than block size. This allows another level of control of benchmarking to the user. Third commit provides support of periodic statistics in memory tests which is not supported currently. It allows to periodically report throughput during memory test run. On the other hand it decreases benchmark throughput roughly by 5% depending on access type and distribution used and underlying hardware. Fourth commit extends sb_rand to use 64-bits variables and functions parameters which allows to use --memory-block-size values larger than 16GB.

[evvoevod]

@akopytov ping...

[zincentimeter]

I faced the broken gaussian problem today and it took me a very great time to get down to the root cause:( Hope this PR can get into main stream ASAP.

[evvoevod]

@akopytov, could you please review these patches? Random memory access patterns are broken.