t_client.sh: Add prepare/cleanup possibilties for each test case

By adding PREPARE_$NUM and CLEANUP_$NUM variables containing command lines
to execute before and after the test case is run.

Signed-off-by: David Sommerseth <davids@redhat.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1384615074-22345-1-git-send-email-dazo@users.sourceforge.net>
URL: http://article.gmane.org/gmane.network.openvpn.devel/7990
Signed-off-by: Gert Doering <gert@greenie.muc.de>