Scripts should not fail if it can't change group on files

[Nicklas Nordborg]

See #1174. This implemented a 'chgrp' command to allow external data to be shared to a specific group based on the prefix used on the sample names. However, if the 'chgrp' command fails (for example if the specified group doesn't exists or is inaccessible for the current user), the entire script fails and results will not be imported back into BASE.

This is a bit unfortunate since the failure can typically be fixed easily by a superuser on the file server and there is really no need to have to delete and re-run the analysis.