Deleted undefined constant
fix an issue of nightly build error
- add sleep to 'Scenario: kill a switch'
fix an issue of nightly build error
- add sleep to 'Scenario: trema killall'
Merge pull request #332 from shun159/feature/pio_arp_simple_router

Deleted undefined constant
fixed processing of sigterm handler
refactoring of hash_core()
disable cookie transaction of switch-daemon
refactoring of external_callback
- support multiple callbacks