Extend the support of --bt5-path= argument to support multiple values like:

 --bt5-path=bt5/folder/0,bt5/folder/3,another/bt5

Values split by Comma format was choose because it is already used by run_only and update_only. 



git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@33196 20353a03-c40f-0410-a6d1-a30d3c3de9de