Test suite: better debug info when the cluster is unexpectedly unhealthy.

Test suite: better debug info when the cluster is unexpectedly unhealthy.

cluster_is_healthy() is now run locally in tests and internally causes
_cluster_is_healthy() to be run on node 0.  When it detects that the
cluster is unhealthy and $ctdb_test_restart_scheduled is not true,
debug information is printed.  This replaces the previous use of
$CTDB_TEST_CLEANING_UP.

To avoid spurious debug on expected restarts, added scheduled
restarts to several tests.

Signed-off-by: Martin Schwenke <martin@meltin.net>