WIP: Vault End-Point Get/Head Update

DONE:
- Vault Head returns whether or not a Vault Exists
- Vault Get returns statistics on the vault
 - statistics are gathered from the drivers
 - drivers are all stubbed out (at present)
 - sqlite driver provides implementation

TODO:
- Implement MongoDB, Cassandra, Swift, and Disk Storage driver statistics
- Update/Add Tests to complete code coverage
@TheSriram - So I originally had the self._conn.execute() and related exception (initially I only had StopIteration) down in the code area itself. It complained there. I refactored it into the above to remove redundancy and improve re-use. Using the same model in the other drivers to the extent I can (at least, the Cassandra driver does well with it; still trying to figure out how to make the queries in MongoDB).

To have the exception work done outside in the other functions, will still yield the same - it pushes them up the stack, but then replicates more code.

To have the exception checks down up higher (as I originally did) is more code yet. And no, you can't just have 1 try/except block as you may lose data - e.g. there may be blocks but no files yet kind of thing.

I'm not too fond of just removing the try/except block either as then there's no way to really set the default value.

The above is nice and clean; coverage just doesn't like it.