monitor: send SIGTERM to the container when SIGHUP is received

monitor: send SIGTERM to the container when SIGHUP is received

For the ->execute() case, we want to make sure the application dies when
SIGHUP is received. The next patch will ignore SIGHUP in the lxc monitor,
because tasks inside the container send SIGHUP to init to have it reload
its config sometimes, and we don't want to do that with init.lxc, since it
might actually kill the container if it forwards SIGHUP to the child and
the child can't handle it.

Signed-off-by: Tycho Andersen <tycho@tycho.ws>