ugly fix: if stdout is missing after cloud-execution, do not abort, but use 0 as returnvalue and warn the user. This allows to parse the logfile for status and stats, even if measuring failed in the cloud.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13809 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c