tst-kill runs various signal handlers, which we run in separate threads.
When the test completes, we may be unlucky enough for the last signal
handler to still be running, at which point when the module's memory
is unmapped (e.g., in test.py -s each test is unmapped when it ends)
we can get a page fault and a crash.

This patch sleeps for a second at the end of tst-kill, to make sure that
the signal handler has completed; This sleep is a bit ugly, but I can't
think of a cleaner way - Posix provides no way to check if there's a
running handler, and I wouldn't like to add a new API just for this test.

Fixes #249.

Reviewed-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>