The go runtime won't always reinstall the default signal handler on the
SIGTERM path, so it's possible the signal won't terminate the process.
Instead, force SIG_DFL for the signal.
The functionality in pkg/osutil ensures that all interrupt handlers finish
and the process kills itself with the proper signal.
Test for interrupt handling added.
The server shutsdown gracefully by stopping on interrupt (Issue #2277.)
Gyuho Lee