There are several scenarios where it can be useful hook into nodepool
after an image got uploaded but before it is taken into use by the
launchers. One use case is to be able to run validations on the image
(e.g. image size, boot test, etc.) before nodepool tries to use that
image and causing potentially node_failures. Another more advanced use
case is to be able to pre-distribute an image to all compute nodes in
a cloud before an image is used at scale.
To facilitate these use cases this adds a new config option
post-upload-hook to the provider config. This takes a path to a user
defined executable script which then can perform various tasks. If the
process fails with an rc != 0 the image gets deleted again and the
upload fails.
Change-Id: I099cf1243b1bd262b8ee96ab323dbd34c7578c10
0dc40d33e4