Log when truncindex.Get returns >1 container

When the user is not using the full hash to retrieve a container it's
possible that we find conflicts with the ids of other containers.

At the moment it's just failing saying that it can not find a container,
but it doesn't say why. Adding a small log saying that duplicates where
found is going to help the user.

Closes #8098
This does not work how you think it works because err is getting redeclared within the scope.  See this small sample to explain the issue. 

http://play.golang.org/p/-AFLBKLQNO

You will have to refactor this more like @LK4D4 said, just keep it explicit so there is no guessing as to what is going on even if it means more code.