Use xxhash instead of fnv

This commit changes the basic hash function for the key value store. It
also fixes build errors due to API changes.

Change-Id: I3849a0a99b556e01c69e5f0a36d933c396c175c3
Fix invalid error codes returned in commit

Change-Id: I6753d947e5432ac3c6dcf0617ba3c44ce0113f18