helper: use return code from docker run for reproduce, run_fuzzer.
helper: use return code from docker run for reproduce, run_fuzzer.

Fixes #1246.

google/oss-fuzz,robertswiecki/oss-fuzz,skia-dev/oss-fuzz,robertswiecki/oss-fuzz,googlefonts/oss-fuzz,google/oss-fuzz,FeliciaLim/oss-fuzz,FeliciaLim/oss-fuzz,google/oss-fuzz,robertswiecki/oss-fuzz,robertswiecki/oss-fuzz,robertswiecki/oss-fuzz,robertswiecki/oss-fuzz,skia-dev/oss-fuzz,google/oss-fuzz,robertswiecki/oss-fuzz,google/oss-fuzz,skia-dev/oss-fuzz,googlefonts/oss-fuzz,skia-dev/oss-fuzz,skia-dev/oss-fuzz,skia-dev/oss-fuzz,google/oss-fuzz,googlefonts/oss-fuzz,FeliciaLim/oss-fuzz,google/oss-fuzz,robertswiecki/oss-fuzz,googlefonts/oss-fuzz,google/oss-fuzz,google/oss-fuzz,robertswiecki/oss-fuzz,robertswiecki/oss-fuzz,FeliciaLim/oss-fuzz,googlefonts/oss-fuzz,FeliciaLim/oss-fuzz,robertswiecki/oss-fuzz,googlefonts/oss-fuzz,googlefonts/oss-fuzz,skia-dev/oss-fuzz,googlefonts/oss-fuzz,skia-dev/oss-fuzz,google/oss-fuzz,google/oss-fuzz,skia-dev/oss-fuzz,googlefonts/oss-fuzz,skia-dev/oss-fuzz,skia-dev/oss-fuzz,googlefonts/oss-fuzz