HPCC-11760 Fix getTargetClusterInfo() in workunit.cpp

The getTopologyCluster() changed recently to not return the 'conn'
for environment data. The getTargetClusterInfo() and another
method are broken by that change. I fix it now.

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>
Merge pull request #6108 from wangkx/fix_getTargetClusterInfo

HPCC-11760 Fix getTargetClusterInfo() in workunit.cpp

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>