cerbero: Use check_output for fetching the perl version
cerbero: Use check_output for fetching the perl version

When running under a locale that the system does not support, perl
prints various warnings to stderr which are accidentally captured by
this and lead to an invalid perl version being set.

atsushieno/cerbero,fluendo/cerbero,nirbheek/cerbero,nirbheek/cerbero,atsushieno/cerbero,fluendo/cerbero,nirbheek/cerbero,GStreamer/cerbero,fluendo/cerbero,nirbheek/cerbero,fluendo/cerbero,atsushieno/cerbero,atsushieno/cerbero,GStreamer/cerbero,GStreamer/cerbero,fluendo/cerbero,GStreamer/cerbero,GStreamer/cerbero,atsushieno/cerbero