cmd-cloud-prune: set default project when unspecified

Updated the project assignment to default to fedora-coreos-cloud when
gcp.get(project) returns None or an empty value. We have a few builds
where the project is not specified.This ensures a fallback project is always
available.

Author: gursewak1997

src/cmd-cloud-prune

@@ -347,7 +347,7 @@ def delete_gcp_image(build, cloud_config, dry_run):
         print(f"No GCP image to prune for {build.id} for {build.arch}")
         return errors
     gcp_image = gcp.get("image")
-    project = gcp.get("project")
+    project = gcp.get("project") or "fedora-coreos-cloud"
     json_key = cloud_config.get("gcp", {}).get("json-key")
     if dry_run:
         print(f"Would delete {gcp_image} GCP image for {build.id}")