NSBperf: fix bad sigint handler

NSBperf: fix bad sigint handler

This is why we don't do things at module
import time.

when we import this module it makes a bad
sigint handler.  Only load signal handlers
at runtime.

Also fix handler to take *args, **kwargs.

Unittest failures:

>     time.sleep(0.01)
E     TypeError: handler() takes 0 positional arguments but 2 were given

Change-Id: I4296a4bdef0e5f4d58b0503dcbc834f3bef0feeb
Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>