Initial checkin for contrail storage stats daemon
    1. added unit tests
    2. renamed/restructured SConscript files
    3. restructured setup.py
    4. added stats-daemon.conf
    5. added test packages in SConscript
    6. modified storage_nodemgr.py based on review comments
    7. added latency changes
    8. added diff logic for read/write bytes/counts for gui
    9. added --conf_file option during daemon init
    10. removed storage_nodemgr.py install in /usr/bin
    11. added contrail-storage-stats console script path in
        storage stats upstart
    12. removed /usr/bin/python from upstart file since it
        was not needed

Change-Id: Ib9ef706d9c790a170050b6bca4cef0e754560acb