Vault End-Point Get/Head Update

CBDEUCE-89, CBDEUCE-111, CBDEUCE-112, CBDEUCE-113, CBDEUCE-114, CBDEUCE-115

DONE:
- Vault Head returns whether or not a Vault Exists
- Vault Get returns statistics on the vault
 - statistics are gathered from the drivers

Note: There are still several coverage issues in the drivers regarding how default values are returned.
deuce.drivers.cassandra.cassandrametadatadriver - lines 198-199
deuce.drivers.sqlite.sqlitemetadatadriver - lines 260-264
deuce.drivers.mongodb.mongodbmetadatadriver - lines 64,73, 82
deuce.drivers.swift.swiftstoragedriver - lines 86-87

Any suggestions on a good resolution welcome.

@TheSriram - actually, see L61-62. That's already taken care of.

The code initializes the structure for what will be returned, then fetches the data and updates it based on what is returned from Swift. The only thing that might be missing in the case of a ClientException would be the 'internal' data where I stored the 'x-timestamp' of the last modification time for the Vault.