Reduce log-level of invalid hintfile message

Fixes #164

This is not uncommon, and is not cause for alarm, so we shouldn't scare
users with an 'error' level log message.
Reduce log-level of more hintfile messages

See previous commit for more detail.
Merge pull request #164 from basho/feature/invalid-hintfile-error-message-level

Invalid hintfile error message is too severe

Reviewed-by: evanmcc