[#101] Add block size parameter for put operation on minicluster

In some tests snakebite depends on number of test data blocks, original
tests were writing big amount of data to get required number of blocks.
Make it possible to change default block 128MB, it will allow to much
easier change number of data file blocks and hopefully increase test
speed.

Closes #101
Merge pull request #102 from ravwojdyla/fix_travis

[#101] Add block size parameter for put operation on minicluster