Need better documentation and error handling with cbrestore

When using cbrestore, there is very little feedback to the user in the event that it is used incorrectly.

I'm sure there are more examples (and therefore we need to test - and try to break - all of the different parameters). For example, when supplying a -u and -P (username/password), but pointing cbrestore at a single-bucket Moxi (which is not expecting a user/pass), there's no feedback that it's not working.