HPCC-11072 Add total time for roxie and hthor

The existing code calculates "Total thor time" for thor
cluster by adding all of graph times togethor. In this
fix, similar to the "Total thor time" for thor, "Total
cluster time" is calculated for both roxie and hthor.
Both "Total thor time" and "Total cluster time" are
reported inside the WsWorkunits.WUINfo response using
new name: "TotalClusterTime".

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>
HPCC-11072 set returned values to 0 if not available

In the getWorkunitTotalTime(), if the requested stats
values are not available, set the returned values to 0.

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>
Merge pull request #6521 from wangkx/h11072

HPCC-11072 Add total time for roxie and hthor

Reviewed-By: Gordon Smith <gordon.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>