Reduce running time of test_different_sizes

Unit test test_different_sizes from RealFilePartitioningTestCase tests
26 variants of partitions sizes and applies each of them to a file,
therefore running time of this test more than 30s. This patch reduce
variants to some "typical", running time now about 5s.

Change-Id: I072666009f4ecca51e84a6dc71257d725aaf2f42
Merge "Reduce running time of test_different_sizes"