cascache.py: Add push info detailing which remote is being pushed to

Work towards fixing issue #275

buildstream/_artifactcache/cascache.py

@@ -258,10 +258,12 @@ class CASCache(ArtifactCache):
         push_remotes = [r for r in self._remotes[project] if r.spec.push]
 
         pushed = False
-
+        
         for remote in push_remotes:
             remote.init()
 
+            element.info("Pushing {} -> {}".format(element._get_brief_display_key(), remote.spec.url))
+
             try:
                 for ref in refs:
                     tree = self.resolve_ref(ref)
@@ -275,7 +277,8 @@ class CASCache(ArtifactCache):
 
                         if response.digest.hash == tree.hash and response.digest.size_bytes == tree.size_bytes:
                             # ref is already on the server with the same tree
-                            continue
+                            element.info("Skipping {}, remote ({}) already has artifact cached".format(element._get_brief_display_key(), remote.spec.url))
+                            continue                            
 
                     except grpc.RpcError as e:
                         if e.code() != grpc.StatusCode.NOT_FOUND: