The new flow:
1) Provision the instance
2) Tear down the instance, but keep the boot disk
3) Create an image from the disk
4) Tear down the disk
The step to update gcloud is no longer needed, since gceimagebundle isn't used anymore.
Fixes#1507 and addresses https://github.com/mitchellh/packer/issues/1447#issuecomment-61610235.
Within GCE, images may be shared across projects. Prior to this
commit, there was no way to inform the GCE builder that a source
image belonged to a specific project. This adds an optional
'source_image_project_id' key to the GCE builder config.
Also fixed the error message to be clear that the image was not found in any of
the projects that we attempted to search, rather than keep the error message
from the last project, which may be confusing to users.
Dustin Carlino
Eric Johnson
Evan Brown
Misha Brukman
Mitchell Hashimoto
Matt Page
Jessica Frazelle
Zac Shenker