Update ChoiceParameterDefinition

The "it.value" don't exist, so we need to set the defaultParameterValue. 

It help me display correctly parameter for my multilauncher plugin. 
Note that other ParameterDefinition use the default value to display parameter, so IMO it is safe to do this.
Merge pull request #1463 from intelradoux/patch-1

Update ChoiceParameterDefinition