scenario001 would install successfully but run out of RAM during
the tempest run.
Create a third scenario and rebalance configuration across these
three different tests.
Additionnally, use the new --service-workers parameter to hardcode
"2" instead of defaulting to $::processorcount which is 8 in the gate
to lower memory usage.
Change-Id: I92a3f45766d45d6a7ee34f0ff306cf67c26e34f6