Creating most google cloud resources uses the compute_operation to
wait for the creation to complete. However, the computeOperationWait*
functions always uses the global `config.Project`, instead of the resource-
specific one.
This means that creating resource in a project other than the main one
fails with a 404 on the operation resource.
This patch uses the project from google_compute_instance instead of the
global one.
This is the first step in removing the config dependency on "project".
This change is backwards-compatible because the value for this new
attribute defaults to the value from the provider.
Common metadata state is now stored
Optimistic locking support added to common_metadata
Revisions to keys in project metadata are now reflected in the project state
Wrote tests for project metadata (all pass)
Relaxed test conditions to work on projects with extra keys
Added documentation for project metadata
