Fix datasource path handling

According to python doc, os.path.join() will throw away all arguments before an argument looking like an absolute path. In my case join("/etc/shinken/SNMP","/Default*.ini") resulted in "/Default*.ini" instead of "/etc/shinken/SNMP/Default*.ini".

This small patch fixes this bug.

Best regards,

N-Mi.
Merge pull request #4 from N-Mi/96ba9bf5c88690aed23e45d244b6702cc51ec7fd

Fix datasource path handling