Only generate valid placeholders
Only generate valid placeholders

We must only use valid placeholders as teamcity uses these as
requirements for the agents.

gradle/gradle,blindpirate/gradle,gradle/gradle,blindpirate/gradle,blindpirate/gradle,blindpirate/gradle,blindpirate/gradle,blindpirate/gradle,gradle/gradle,gradle/gradle,gradle/gradle,gradle/gradle,blindpirate/gradle,blindpirate/gradle,gradle/gradle,gradle/gradle,gradle/gradle,gradle/gradle,blindpirate/gradle,blindpirate/gradle