HPCC-11398 Spray file using NodeGroup and change related display

Read and display node group as spray target to thor cluster;
Rename related variables/methods from 'cluster' to 'NodeGroup';
Rename the variable 'DFUQRFcluster' to 'DFUQRFnodegroup' and rename
the variable 'DFUQRFgroup' to 'DFUQRFnodegroups';
Rename the 'Cluster' column to 'NodeGroup' on Browse Logical File
page.

Signed-off-by: Kevin Wang kevin.wang@lexisnexis.com