Fix EC2 not found errors for volumes and snapshots.
Fix EC2 not found errors for volumes and snapshots.

According to AWS docs
(http://docs.aws.amazon.com/AWSEC2/latest/APIReference/
api-error-codes.html)

Change-Id: I43af230b975263bb2a14e0cc0bd8718f55bd8a55
Closes-Bug: #1323813

openstack/oslo.versionedobjects,citrix-openstack-build/oslo.versionedobjects