Rewrite Rename backend in a more atomic fashion

Move the core of renaming logic into the DB. This guarantees a
lot more atomicity than we have right now (our current solution,
removing the container from the DB and re-creating it, is *VERY*
not atomic and prone to leaving a corrupted state behind if
things go wrong. Moving things into the DB allows us to remove
most, but not all, of this - there's still a potential scenario
where the c/storage rename fails but the Podman rename succeeds,
and we end up with a mismatched state.

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

libpod/in_memory_state.go

@@ -822,6 +822,46 @@ func (s *InMemoryState) RewriteContainerConfig(ctr *Container, newCfg *Container
 	return nil
 }
 
+// SafeRewriteContainerConfig rewrites a container's configuration.
+// It's safer than RewriteContainerConfig, but still has limitations. Please
+// read the comment in state.go before using.
+func (s *InMemoryState) SafeRewriteContainerConfig(ctr *Container, oldName, newName string, newCfg *ContainerConfig) error {
+	if !ctr.valid {
+		return define.ErrCtrRemoved
+	}
+
+	if _, err := s.nameIndex.Get(newName); err == nil {
+		return errors.Wrapf(define.ErrCtrExists, "name %s is in use", newName)
+	}
+
+	// If the container does not exist, return error
+	stateCtr, ok := s.containers[ctr.ID()]
+	if !ok {
+		ctr.valid = false
+		return errors.Wrapf(define.ErrNoSuchCtr, "container with ID %s not found in state", ctr.ID())
+	}
+
+	// Change name in registry.
+	if s.namespace != "" {
+		nsIndex, ok := s.namespaceIndexes[s.namespace]
+		if !ok {
+			return define.ErrInternal
+		}
+		nsIndex.nameIndex.Release(oldName)
+		if err := nsIndex.nameIndex.Reserve(newName, ctr.ID()); err != nil {
+			return errors.Wrapf(err, "error registering name %s", newName)
+		}
+	}
+	s.nameIndex.Release(oldName)
+	if err := s.nameIndex.Reserve(newName, ctr.ID()); err != nil {
+		return errors.Wrapf(err, "error registering name %s", newName)
+	}
+
+	stateCtr.config = newCfg
+
+	return nil
+}
+
 // RewritePodConfig rewrites a pod's configuration.
 // This function is DANGEROUS, even with in-memory state.
 // Please read the full comment on it in state.go before using it.