prerequisites for DAS keyword search

in das.spec, the Source0 is changed ONLY temporarily to point to keyword search development branch.
Once the keyword search is merged into DAS master, Source0 will be restored to point to main DAS repository

recently added:
* made sure setuptools don't download any dependencies. this resulted in adding another dependency (needed by py2-jsonpath): py2-six.spec (which is a module for python 2-3 compatibility)