Time stamp filter for log output

For inspection of solver output, it could be useful to run the stdout lines through a filter that
adds time stamps as prefix, like in syslog.

Problem: Some verifiers do this already themselves.
Example: https://sv-comp.sosy-lab.org/2017/results/results-verified/uautomizer.2017-01-13_1241.logfiles/sv-comp17.array_false-unreach-call_true-termination.i.log