Reduce SLICE_DB_UPDATE_INTERVAL to 5 sec

SLICE_DB_UPDATE_INTERVAL 30 sec is too long if slice members
are maintained by an automated system like IaaS infrastructure.
This commit is just a work-around, and ideally slice db reloading
should be done more inteligently like inotifiy.

Also reduces FILTER_DB_UPDATE_INTERVAL to 5 sec.
Merge pull request #42 from amotoki/shorten-slice-db-reloading

Reduce SLICE_DB_UPDATE_INTERVAL to 5 sec