fix for promotion/downstreamParameterized/currentBuild

a promoted-builds action of downstreamParameterized
is creating the wrong type of buildSteps;
it is creating `hudson.plugins.parameterizedtrigger.TriggerBuilder`
instead of the buildStep that the web ui creates,
`hudson.plugins.parameterizedtrigger.BuildTrigger`

this subtle difference breaks the expected behavior of
passing the current build parameters via `currentBuild()`
in DSL, resulting in no parameters being passed

this fix overrides the behavior of
`AbstractStepContext#downstreamParameterized`
to behave like the PublisherContext#downstreamParameterized by
calling `DownstreamContext#createDownstreamNode(false)`