[Cloud SQL Proxy] Fix metadata key for additional instances (#254)
[Cloud SQL Proxy] Fix metadata key for additional instances (#254)

See more details here: https://stackoverflow.com/a/44938499
GoogleCloudDataproc/initialization-actions,dennishuo/dataproc-initialization-actions,GoogleCloudDataproc/initialization-actions,GoogleCloudDataproc/initialization-actions,lukeFalsina/dataproc-initialization-actions,dennishuo/dataproc-initialization-actions,lukeFalsina/dataproc-initialization-actions