Limit the heap size of the VerifierCloud benchmark client
when submitting the benchmarks to the cloud.
The heap size is calculated depending on the number of submitted runs,
so hopefully it works with small as well as with large run collections.
The reduction is necessary to reduce the load on the BuildBot machine.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13379 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c