Improve log for Kaggle Cache Resolver.

[rosbo]

• Clarifiy whether the user is accessing a single file or the full model.
• Do not print "Mounting files ..." if the model is already mounted.
• Remove the "Model X is attached" at the end. The method returning the path is already enough. This is spammy.

The goal is to reduce the spammy log since Keras will be attaching several files.

• Before: https://screenshot.googleplex.com/4KvivYGDqVxCngc
• After: https://screenshot.googleplex.com/9YPyQG5oW5B87iS