Sample Size should be configurable

[kuzeko]

We may want to run experiments with different sample size.
Currently this is configured in the header.groovy file

graph-databases-testsuite/runtime/tp2/header.groovy.sh

Line 92 in 916a3db

N = 10;

graph-databases-testsuite/runtime/tp3/header.groovy.sh

Line 108 in 36eab84

N = 10;

This option should be configurable, but of course the LID files should be checked for consistency