test/eas/rfc: fix calculation of the first period of the task
Created by: JaviMerino
We avoid the first period of the rtapp task in the boosted utilization signal test because of the initial high load. The period we read from the parameters is expressed in milliseconds but the index of the dataframes returned by trappy is in seconds. Convert rtapp_period to seconds before adding it to task_start to correctly add the two variables in the same unit (seconds).