Fix suppressing running the UpdatePRService steps

[mconnew]

Converted the _RunWithCoreWcfService from a variable into a parameter. The variable defined on the pipeline definiton was being overwritten by the yml file so wasn't actually applying. If you look at existing CoreWCF runs in the run tests step, you'll see that _RunWithCoreWcfService is being set to false instead of the expecgted true.

The pipeline definition will need to be edited to remove the variable, instead it becomes a check box like shown here:

This can't be done until after this change is merged. I manually kicked off a dotnet-wcf-with-corewcf--ci pipeline run with this new parameter checked which validates this PR. It's the only way to apply the parameter before this is merged as the existing pipeline definition can't see the parameter as it's not merged, so can't be edited to check that box until post merge.
https://dev.azure.com/dnceng-public/public/_build/results?buildId=820662&view=results