Initial checkin for contrail storage stats daemon [review changes]
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: I22d539cd7f054e10fac5b6da5f5446d849ce96ee