In the benchmark script, do not round any measured values.
Instead, round when generating the HTML tables.

Rounding should be done only once and at the latest moment possible
to minimize errors.
Also we should round only values that are intended to be read by humans.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13486 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c