use ParseRepositoryTag instead on split on : in imagedelete
add ParseRepositoryTag tests
add regression tests
fix #1314 discard error when loading old container format
improve tests
fix same issue in api.go
Merge pull request #1334 from dotcloud/1314-compat_broke-fix

Discard error when loading old container format
Merge pull request #1328 from dotcloud/1307_url_port_delete-fix

Use utils.ParseRepositoryTag instead of strings.Split(name, ":") in server.ImageDelete