adding support for eucalyptus 

Hi,

Following patch add support eucalyptus. It adds service_path configuration for folks who use Eucalyptus walrus without DNS and takes care of create_request a bit to make it work for Eucalyptus.

Tested against Eucalyptus 4.0.0 that uses a new object storage gateway with backend riakcs but should work for s3 and walrus as well.

Please let me know if there are any questions. I am happy to test with this patch against S3 to ensure nothing is broken if you have any test cases.

Cheers!
Deependra