Allows signature matches for messages that don't sign the /services/Walrus portion of the url. Fixes EUCA-5275

WalrusAuthenticationHandler checks the signature of the string-to-sign using the full service path:
/services/Walrus/<bucket>/<object>

If that fails it then recalculates a signature using the shortened path:
/<bucket>/<object>

This is intended to increase tool compatibility in tools that only sign using '/' + bucket + '/' + object