Added use of $ctdb_test_exit_hook to function ctdb_test_exit. Removed

Added use of $ctdb_test_exit_hook to function ctdb_test_exit.  Removed
sleeps from ban/unban tests.  Now expect "ctdb ping" to return false
if it fails, so made relevant change to 09_ctdb_ping.sh.  New
functions install_eventscript and uninstall_eventscript.  New
setup/cleanup tests 00_ctdb_install_eventscript.sh and
99_ctdb_uninstall_eventscript.sh.  New test 21_ctdb_disablemonitor.sh,
which is incredibly complex.

Signed-off-by: Martin Schwenke <martin@meltin.net>
(This used to be ctdb commit 23bffef2295772f5b795236d60b7fb6ea754b7fb)