HPCC-11229 - Fix testLocalCluster dfu check

Ensure nodeGroup is checked against target groupname, by using
existing helper method getClusterGroupName

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #5697 from jakesmith/hpcc-11229

HPCC-11229 - Fix testLocalCluster dfu check

Reviewed-By: Attila Vamos <attila.vamos@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>