Restore 'deployments' key to cfn Metadata

In recent changes support was added to explode the deployment key into
multiple json files for merging by os-apply-config. But this breaks
other users who want direct access to the full deployments structure.

There seems to be no real reason to delete the key other than tidiness,
so we will stop deleting it from the main cfn structure.

Change-Id: Icf9479376e32c3ad8f9be29359e6100c1aeda2a5
Closes-Bug: #1299110
Merge "Restore 'deployments' key to cfn Metadata"