HPCC-9183 change the 'cluster stopped' to 'cluster not attached'

When a cluster is not in /Status/Servers list, ECLWatch Activity page
shows a message 'cluster stopped' beside the cluster name. It has been
suggested that the message should say 'cluster not attached'.

Signed-off-by: Kevin Wang <kevin.wang@lexisnexis.com>
Merge pull request #4279 from wangkx/h9183a

HPCC-9183 change the 'cluster stopped' to 'cluster not attached'

Reviewed-By Richard Chapman <rchapman@hpccplatform.com>