balloon: capture exception if the monitor can't start

At least in its current incarnation, it is risky to start the balloon without
the monitor. Tomek found a problem under which a problem with Tomcat's logging
system would cause an exception to be thrown.

While we were mistaken about the effects of that problem, namely, the exception
seems to caught by the logger itself and won't affect the functioning of the
monitor, it drew our attention to the fact that exceptions do can happen. And if
they do, we should be prepared to catch them and abort.

Reviewed-by: Tomasz Grabiec <tgrabiec@gmail.com>
Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>