Support delayed/lazy configuration

[staffanf]

Use case: We want to be able to build locally with minimal user configuration after checkout.

Current situation: The artifactory DSL calls it publish closure at configuration time and this makes it hard for user to only pupulate the needed properties when they are required.
A user that does not have publisher permission does not need to populate these properties.

artifactory {
  publish {
    repository {
      repoKey = "${artifactoryPublishRepo}"
      username = "${artifactory_user}"
      password = "${artifactory_password}"
    }
  }
}

Suggestion: Allow lazy configuration that is only resolved when the related artifactory tasks is executed.
This should be the default for all configuration.