p.haul: use /usr/bin/env instead of /bin/env

Some systems don't have /bin/env. But most
systems have /usr/bin/env, so lets use it in
shabang.

Reported-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Reported-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Ruslan Kuprieiev <kupruser@gmail.com>
Acked-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>