Added hostIdentifier to info output

Small change that adds the the hostIdentifier in the output to the info log when running queries.

Also, wraps the `DBHandle::getInstance()` call in a try block, an cause the `getHostIdentifier()` function to throw an error if it cant access the DB.
I'm not sure how I feel about this being an exception. I'd rather either fallback to some sane option (like hostname) and appropriately log (what's there now) or return the `osquery::Status` object and modify the caller to gracefully handle it. Was there a specific reason that you changed this to be an exception?