tests: Update integration.sh to use TEST_VAR_DIR

tests: Update integration.sh to use TEST_VAR_DIR

There are 2 subtleties:

* Local daemons currently use the in-tree tests/events.d/ subdirectory
  for their eventscripts.  However, some tests install/remove test-specific
  eventscripts so now $TEST_VAR_DIR/events.d/ is used and the standard
  eventscripts are copied there at setup time.

* The pgrep/pkill logic for killing local daemons currently relies on
  ctdbd being run with a full path to tests/bin/ctdbd.  If the tests
  are installed and run against an installed daemon then this won't
  work.  Therefore, ctdbd is now expected to be in $PATH and is
  found/killed by matching:

    ctdbd --socket=.* --nlist .* --nopublicipcheck

  This is complex but should avoid killing a real ctdbd running on a
  node.

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