Use packageImage as builder image fingerprint

This allows to have an unique identifier for the builder image id against
different depgraphs combinations. The package fingerprint is not enough,
as an atom could have a difference deptree depending on the requires
constraints.

TODO: Don't use the full image name, but only the hash as a salt
(currently the salt contains ALSO a reference of the image-repository,
as such it doesn't allow to port a tree in a different docker registry)

cmd/tree/validate.go

@@ -184,7 +184,7 @@ func validateWorker(i int,
 					))
 
 					// Check if the solver is already been done for the deep
-					_, err := cacheDeps.Get(r.HashFingerprint())
+					_, err := cacheDeps.Get(r.HashFingerprint(""))
 					if err == nil {
 						Debug("  :direct_hit: Cache Hit for dep",
 							fmt.Sprintf("%s/%s-%s", r.GetCategory(), r.GetName(), r.GetVersion()))
@@ -218,7 +218,7 @@ func validateWorker(i int,
 					}
 
 					// Register the key
-					cacheDeps.Set(r.HashFingerprint(), "1")
+					cacheDeps.Set(r.HashFingerprint(""), "1")
 
 				}
 			}