Shared VPC allows user to create resources on a network which lives in another project than the project where the resource is being is created.
This allows various service project to share a common VPC network which lives in a host project.
Dataproc provisioner should support configuring network for the provisioner to a shared VPC network i.e. a network which lives in another project. Currently it only looks into network which reside in the project where the Dataproc cluster will be launched.